diff --git a/download_from_google_storage.py b/download_from_google_storage.py
new file mode 100755
index 000000000..b1891755d
--- /dev/null
+++ b/download_from_google_storage.py
@@ -0,0 +1,339 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Download files from Google Storage based on SHA1 sums."""
+
+
+import hashlib
+import optparse
+import os
+import Queue
+import re
+import sys
+import threading
+import time
+
+import subprocess2
+
+
+GSUTIL_DEFAULT_PATH = os.path.join(
+    os.path.dirname(os.path.abspath(__file__)),
+    'third_party', 'gsutil', 'gsutil')
+
+
+class FileNotFoundError(IOError):
+  pass
+
+
+class InvalidFileError(IOError):
+  pass
+
+
+# Common utilities
+class Gsutil(object):
+  """Call gsutil with some predefined settings.  This is a convenience object,
+  and is also immutable."""
+  def __init__(self, path, boto_path=None, timeout=None):
+    if not os.path.exists(path):
+      raise FileNotFoundError('GSUtil not found in %s' % path)
+    self.path = path
+    self.timeout = timeout
+    self.boto_path = boto_path
+
+  def call(self, *args):
+    env = os.environ.copy()
+    if self.boto_path:
+      env['AWS_CREDENTIAL_FILE'] = self.boto_path
+    return subprocess2.call((sys.executable, self.path) + args,
+                            env=env,
+                            timeout=self.timeout)
+
+  def check_call(self, *args):
+    env = os.environ.copy()
+    if self.boto_path:
+      env['AWS_CREDENTIAL_FILE'] = self.boto_path
+    ((out, err), code) = subprocess2.communicate(
+        (sys.executable, self.path) + args,
+        stdout=subprocess2.PIPE,
+        stderr=subprocess2.PIPE,
+        env=env,
+        timeout=self.timeout)
+
+    # Parse output.
+    status_code_match = re.search('status=([0-9]+)', err)
+    if status_code_match:
+      return (int(status_code_match.group(1)), out, err)
+    if ('You are attempting to access protected data with '
+          'no configured credentials.' in err):
+      return (403, out, err)
+    if 'No such object' in err:
+      return (404, out, err)
+    return (code, out, err)
+
+
+def check_bucket_permissions(bucket, gsutil):
+  if not bucket:
+    print >> sys.stderr, 'Missing bucket %s.'
+    return (None, 1)
+  base_url = 'gs://%s' % bucket
+
+  code, _, ls_err = gsutil.check_call('ls', base_url)
+  if code == 403:
+    code, _, _ = gsutil.call('config')
+    if code != 0:
+      print >> sys.stderr, 'Error while authenticating to %s.' % base_url
+  elif code == 404:
+    print >> sys.stderr, '%s not found.' % base_url
+  elif code != 0:
+    print >> sys.stderr, ls_err
+  return (base_url, code)
+
+
+def get_sha1(filename):
+  sha1 = hashlib.sha1()
+  with open(filename, 'rb') as f:
+    while True:
+      # Read in 1mb chunks, so it doesn't all have to be loaded into memory.
+      chunk = f.read(1024*1024)
+      if not chunk:
+        break
+      sha1.update(chunk)
+  return sha1.hexdigest()
+
+
+# Download-specific code starts here
+
+def enumerate_work_queue(input_filename, work_queue, directory,
+                         recursive, ignore_errors, output, sha1_file):
+  if sha1_file:
+    if not os.path.exists(input_filename):
+      if not ignore_errors:
+        raise FileNotFoundError('%s not found.' % input_filename)
+      print >> sys.stderr, '%s not found.' % input_filename
+    with open(input_filename, 'rb') as f:
+      sha1_match = re.match('^([A-Za-z0-9]{40})$', f.read(1024).rstrip())
+      if sha1_match:
+        work_queue.put(
+            (sha1_match.groups(1)[0], input_filename.replace('.sha1', '')))
+        return 1
+    if not ignore_errors:
+      raise InvalidFileError('No sha1 sum found in %s.' % input_filename)
+    print >> sys.stderr, 'No sha1 sum found in %s.' % input_filename
+    return 0
+
+  if not directory:
+    work_queue.put((input_filename, output))
+    return 1
+
+  work_queue_size = 0
+  for root, dirs, files in os.walk(input_filename):
+    if not recursive:
+      for item in dirs[:]:
+        dirs.remove(item)
+    else:
+      for exclude in ['.svn', '.git']:
+        if exclude in dirs:
+          dirs.remove(exclude)
+    for filename in files:
+      full_path = os.path.join(root, filename)
+      if full_path.endswith('.sha1'):
+        with open(full_path, 'rb') as f:
+          sha1_match = re.match('^([A-Za-z0-9]{40})$', f.read(1024).rstrip())
+        if sha1_match:
+          work_queue.put(
+              (sha1_match.groups(1)[0], full_path.replace('.sha1', '')))
+          work_queue_size += 1
+        else:
+          if not ignore_errors:
+            raise InvalidFileError('No sha1 sum found in %s.' % filename)
+          print >> sys.stderr, 'No sha1 sum found in %s.' % filename
+  return work_queue_size
+
+
+def _downloader_worker_thread(thread_num, q, force, base_url,
+                              gsutil, out_q, ret_codes):
+  while True:
+    input_sha1_sum, output_filename = q.get()
+    if input_sha1_sum is None:
+      return
+    if os.path.exists(output_filename) and not force:
+      if get_sha1(output_filename) == input_sha1_sum:
+        out_q.put(
+            '%d> File %s exists and SHA1 matches. Skipping.' % (
+                thread_num, output_filename))
+        continue
+    # Check if file exists.
+    file_url = '%s/%s' % (base_url, input_sha1_sum)
+    if gsutil.check_call('ls', file_url)[0] != 0:
+      out_q.put('%d> File %s for %s does not exist, skipping.' % (
+          thread_num, file_url, output_filename))
+      ret_codes.put((1, 'File %s for %s does not exist.' % (
+          file_url, output_filename)))
+      continue
+    # Fetch the file.
+    out_q.put('%d> Downloading %s...' % (
+        thread_num, output_filename))
+    code, _, err = gsutil.check_call('cp', '-q', file_url, output_filename)
+    if code != 0:
+      out_q.put('%d> %s' % (thread_num, err))
+      ret_codes.put((code, err))
+
+
+def printer_worker(output_queue):
+  while True:
+    line = output_queue.get()
+    # Its plausible we want to print empty lines.
+    if line is None:
+      break
+    print line
+
+
+def download_from_google_storage(
+    input_filename, base_url, gsutil, num_threads, directory, recursive,
+    force, output, ignore_errors, sha1_file):
+  # Start up all the worker threads.
+  all_threads = []
+  download_start = time.time()
+  stdout_queue = Queue.Queue()
+  work_queue = Queue.Queue()
+  ret_codes = Queue.Queue()
+  ret_codes.put((0, None))
+  for thread_num in range(num_threads):
+    t = threading.Thread(
+        target=_downloader_worker_thread,
+        args=[thread_num, work_queue, force, base_url,
+              gsutil, stdout_queue, ret_codes])
+    t.daemon = True
+    t.start()
+    all_threads.append(t)
+  printer_thread = threading.Thread(target=printer_worker, args=[stdout_queue])
+  printer_thread.daemon = True
+  printer_thread.start()
+
+  # Enumerate our work queue.
+  work_queue_size = enumerate_work_queue(
+      input_filename, work_queue, directory, recursive,
+      ignore_errors, output, sha1_file)
+  for _ in all_threads:
+    work_queue.put((None, None))  # Used to tell worker threads to stop.
+
+  # Wait for all downloads to finish.
+  for t in all_threads:
+    t.join()
+  stdout_queue.put(None)
+  printer_thread.join()
+
+  # See if we ran into any errors.
+  max_ret_code = 0
+  for ret_code, message in ret_codes.queue:
+    max_ret_code = max(ret_code, max_ret_code)
+    if message:
+      print >> sys.stderr, message
+  if not max_ret_code:
+    print 'Success!'
+
+  print 'Downloading %d files took %1f second(s)' % (
+      work_queue_size, time.time() - download_start)
+  return max_ret_code
+
+
+def main(args):
+  usage = ('usage: %prog [options] target\n'
+           'Target must be:\n'
+           '  (default) a sha1 sum ([A-Za-z0-9]{40}).\n'
+           '  (-s or --sha1_file) a .sha1 file, containing a sha1 sum on '
+           'the first line.\n'
+           '  (-d or --directory) A directory to scan for .sha1 files.')
+  parser = optparse.OptionParser(usage)
+  parser.add_option('-o', '--output',
+                    help='Specify the output file name. Defaults to: '
+                         '(a) Given a SHA1 hash, the name is the SHA1 hash. '
+                         '(b) Given a .sha1 file or directory, the name will '
+                         'match (.*).sha1.')
+  parser.add_option('-b', '--bucket',
+                    help='Google Storage bucket to fetch from.')
+  parser.add_option('-e', '--boto',
+                    help='Specify a custom boto file.')
+  parser.add_option('-c', '--no_resume', action='store_true',
+                    help='Resume download if file is partially downloaded.')
+  parser.add_option('-f', '--force', action='store_true',
+                    help='Force download even if local file exists.')
+  parser.add_option('-i', '--ignore_errors', action='store_true',
+                    help='Don\'t throw error if we find an invalid .sha1 file.')
+  parser.add_option('-r', '--recursive', action='store_true',
+                    help='Scan folders recursively for .sha1 files. '
+                         'Must be used with -d/--directory')
+  parser.add_option('-t', '--num_threads', default=1, type='int',
+                    help='Number of downloader threads to run.')
+  parser.add_option('-d', '--directory', action='store_true',
+                    help='The target is a directory.  '
+                         'Cannot be used with -s/--sha1_file.')
+  parser.add_option('-s', '--sha1_file', action='store_true',
+                    help='The target is a file containing a sha1 sum.  '
+                         'Cannot be used with -d/--directory.')
+
+  (options, args) = parser.parse_args()
+  if not args:
+    parser.error('Missing target.')
+  if len(args) > 1:
+    parser.error('Too many targets.')
+  if not options.bucket:
+    parser.error('Missing bucket.  Specify bucket with --bucket.')
+  if options.sha1_file and options.directory:
+    parser.error('Both --directory and --sha1_file are specified, '
+                 'can only specify one.')
+  if options.recursive and not options.directory:
+    parser.error('--recursive specified but --directory not specified.')
+  if options.output and options.directory:
+    parser.error('--directory is specified, so --output has no effect.')
+  input_filename = args[0]
+
+  # Set output filename if not specified.
+  if not options.output and not options.directory:
+    if not options.sha1_file:
+      # Target is a sha1 sum, so output filename would also be the sha1 sum.
+      options.output = input_filename
+    elif options.sha1_file:
+      # Target is a .sha1 file.
+      if not input_filename.endswith('.sha1'):
+        parser.error('--sha1_file is specified, but the input filename '
+                     'does not end with .sha1, and no --output is specified. '
+                     'Either make sure the input filename has a .sha1 '
+                     'extension, or specify --output.')
+      options.output = input_filename[:-5]
+    else:
+      parser.error('Unreachable state.')
+
+  # Check if output file already exists.
+  if not options.directory and not options.force and not options.no_resume:
+    if os.path.exists(options.output):
+      parser.error('Output file %s exists and --no_resume is specified.'
+                   % options.output)
+
+  # Make sure we can find a working instance of gsutil.
+  if os.path.exists(GSUTIL_DEFAULT_PATH):
+    gsutil = Gsutil(GSUTIL_DEFAULT_PATH)
+  else:
+    gsutil = None
+    for path in os.environ["PATH"].split(os.pathsep):
+      if os.path.exists(path) and 'gsutil' in os.listdir(path):
+        gsutil = Gsutil(os.path.join(path, 'gsutil'))
+    if not gsutil:
+      parser.error('gsutil not found in %s, bad depot_tools checkout?' %
+                   GSUTIL_DEFAULT_PATH)
+
+  # Check we have a valid bucket with valid permissions.
+  base_url, code = check_bucket_permissions(options.bucket, gsutil)
+  if code:
+    return code
+
+  return download_from_google_storage(
+      input_filename, base_url, gsutil, options.num_threads, options.directory,
+      options.recursive, options.force, options.output, options.ignore_errors,
+      options.sha1_file)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))
\ No newline at end of file
diff --git a/tests/download_from_google_storage_unittests.py b/tests/download_from_google_storage_unittests.py
new file mode 100755
index 000000000..abf12d991
--- /dev/null
+++ b/tests/download_from_google_storage_unittests.py
@@ -0,0 +1,282 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+# pylint: disable=W0212
+
+"""Unit tests for download_from_google_storage.py."""
+
+import optparse
+import os
+import Queue
+import shutil
+import sys
+import tempfile
+import threading
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+import upload_to_google_storage
+import download_from_google_storage
+
+# ../third_party/gsutil/gsutil
+GSUTIL_DEFAULT_PATH = os.path.join(
+    os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
+    'third_party', 'gsutil', 'gsutil')
+TEST_DIR = os.path.dirname(os.path.abspath(__file__))
+
+
+class GsutilMock(object):
+  def __init__(self, path, boto_path=None, timeout=None):
+    self.path = path
+    self.timeout = timeout
+    self.boto_path = boto_path
+    self.expected = []
+    self.history = []
+    self.lock = threading.Lock()
+
+  def add_expected(self, return_code, out, err):
+    self.expected.append((return_code, out, err))
+
+  def append_history(self, method, args):
+    self.history.append((method, args))
+
+  def call(self, *args):
+    with self.lock:
+      self.append_history('call', args)
+      if self.expected:
+        return self.expected.pop(0)[0]
+      else:
+        return 0
+
+  def check_call(self, *args):
+    with self.lock:
+      self.append_history('check_call', args)
+      if self.expected:
+        return self.expected.pop(0)
+      else:
+        return (0, '', '')
+
+
+class GstoolsUnitTests(unittest.TestCase):
+  def setUp(self):
+    self.temp_dir = tempfile.mkdtemp(prefix='gstools_test')
+    self.base_path = os.path.join(self.temp_dir, 'test_files')
+    shutil.copytree(os.path.join(TEST_DIR, 'gstools'), self.base_path)
+
+  def cleanUp(self):
+    shutil.rmtree(self.temp_dir)
+
+  def test_gsutil(self):
+    gsutil = download_from_google_storage.Gsutil(GSUTIL_DEFAULT_PATH)
+    self.assertEqual(gsutil.path, GSUTIL_DEFAULT_PATH)
+    code, _, err = gsutil.check_call()
+    self.assertEqual(code, 0)
+    self.assertEqual(err, '')
+
+  def test_gsutil_version(self):
+    gsutil = download_from_google_storage.Gsutil(GSUTIL_DEFAULT_PATH)
+    _, _, err = gsutil.check_call('version')
+    err_lines = err.splitlines()
+    self.assertEqual(err_lines[0], 'gsutil version 3.25')
+    self.assertEqual(
+        err_lines[1],
+        'checksum ce71ac982f1148315e7fa65cff2f83e8 (OK)')
+
+  def test_get_sha1(self):
+    lorem_ipsum = os.path.join(self.base_path, 'lorem_ipsum.txt')
+    self.assertEqual(
+        download_from_google_storage.get_sha1(lorem_ipsum),
+        '7871c8e24da15bad8b0be2c36edc9dc77e37727f')
+
+  def test_get_md5(self):
+    lorem_ipsum = os.path.join(self.base_path, 'lorem_ipsum.txt')
+    self.assertEqual(
+        upload_to_google_storage.get_md5(lorem_ipsum),
+        '634d7c1ed3545383837428f031840a1e')
+
+  def test_get_md5_cached_read(self):
+    lorem_ipsum = os.path.join(self.base_path, 'lorem_ipsum.txt')
+    # Use a fake 'stale' MD5 sum.  Expected behavior is to return stale sum.
+    self.assertEqual(
+        upload_to_google_storage.get_md5_cached(lorem_ipsum),
+        '734d7c1ed3545383837428f031840a1e')
+
+  def test_get_md5_cached_write(self):
+    lorem_ipsum2 = os.path.join(self.base_path, 'lorem_ipsum2.txt')
+    lorem_ipsum2_md5 = os.path.join(self.base_path, 'lorem_ipsum2.txt.md5')
+    if os.path.exists(lorem_ipsum2_md5):
+      os.remove(lorem_ipsum2_md5)
+    # Use a fake 'stale' MD5 sum.  Expected behavior is to return stale sum.
+    self.assertEqual(
+        upload_to_google_storage.get_md5_cached(lorem_ipsum2),
+        '4c02d1eb455a0f22c575265d17b84b6d')
+    self.assertTrue(os.path.exists(lorem_ipsum2_md5))
+    self.assertEqual(
+        open(lorem_ipsum2_md5, 'rb').read(),
+        '4c02d1eb455a0f22c575265d17b84b6d')
+    os.remove(lorem_ipsum2_md5)  # Clean up.
+    self.assertFalse(os.path.exists(lorem_ipsum2_md5))
+
+
+class DownloadTests(unittest.TestCase):
+  def setUp(self):
+    self.gsutil = GsutilMock(GSUTIL_DEFAULT_PATH)
+    self.temp_dir = tempfile.mkdtemp(prefix='gstools_test')
+    self.checkout_test_files = os.path.join(
+        TEST_DIR, 'gstools', 'download_test_data')
+    self.base_path = os.path.join(
+        self.temp_dir, 'download_test_data')
+    shutil.copytree(self.checkout_test_files, self.base_path)
+    self.base_url = 'gs://sometesturl'
+    self.parser = optparse.OptionParser()
+    self.queue = Queue.Queue()
+    self.ret_codes = Queue.Queue()
+    self.lorem_ipsum = os.path.join(self.base_path, 'lorem_ipsum.txt')
+    self.lorem_ipsum_sha1 = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    self.maxDiff = None
+
+  def cleanUp(self):
+    shutil.rmtree(self.temp_dir)
+
+  def test_enumerate_files_non_recursive(self):
+    queue_size = download_from_google_storage.enumerate_work_queue(
+        self.base_path, self.queue, True, False, False, None, False)
+    expected_queue = [
+        ('e6c4fbd4fe7607f3e6ebf68b2ea4ef694da7b4fe',
+            os.path.join(self.base_path, 'rootfolder_text.txt')),
+       ('7871c8e24da15bad8b0be2c36edc9dc77e37727f',
+            os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt'))]
+    self.assertEqual(sorted(expected_queue), sorted(self.queue.queue))
+    self.assertEqual(queue_size, 2)
+
+  def test_enumerate_files_recursive(self):
+    queue_size = download_from_google_storage.enumerate_work_queue(
+        self.base_path, self.queue, True, True, False, None, False)
+    expected_queue = [
+        ('e6c4fbd4fe7607f3e6ebf68b2ea4ef694da7b4fe',
+            os.path.join(self.base_path, 'rootfolder_text.txt')),
+        ('7871c8e24da15bad8b0be2c36edc9dc77e37727f',
+            os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt')),
+        ('b5415aa0b64006a95c0c409182e628881d6d6463',
+            os.path.join(self.base_path, 'subfolder', 'subfolder_text.txt'))]
+    self.assertEqual(sorted(expected_queue), sorted(self.queue.queue))
+    self.assertEqual(queue_size, 3)
+
+  def test_download_worker_single_file(self):
+    sha1_hash = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    input_filename = '%s/%s' % (self.base_url, sha1_hash)
+    output_filename = os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt')
+    self.queue.put((sha1_hash, output_filename))
+    self.queue.put((None, None))
+    stdout_queue = Queue.Queue()
+    download_from_google_storage._downloader_worker_thread(
+        0, self.queue, False, self.base_url, self.gsutil,
+        stdout_queue, self.ret_codes)
+    expected_calls = [
+        ('check_call',
+            ('ls', input_filename)),
+        ('check_call',
+            ('cp', '-q', input_filename, output_filename))]
+    expected_output = [
+        '0> Downloading %s...' % output_filename]
+    expected_ret_codes = []
+    self.assertEqual(list(stdout_queue.queue), expected_output)
+    self.assertEqual(self.gsutil.history, expected_calls)
+    self.assertEqual(list(self.ret_codes.queue), expected_ret_codes)
+
+  def test_download_worker_skips_file(self):
+    sha1_hash = 'e6c4fbd4fe7607f3e6ebf68b2ea4ef694da7b4fe'
+    output_filename = os.path.join(self.base_path, 'rootfolder_text.txt')
+    self.queue.put((sha1_hash, output_filename))
+    self.queue.put((None, None))
+    stdout_queue = Queue.Queue()
+    download_from_google_storage._downloader_worker_thread(
+        0, self.queue, False, self.base_url, self.gsutil,
+        stdout_queue, self.ret_codes)
+    expected_output = [
+        '0> File %s exists and SHA1 matches. Skipping.' % output_filename
+    ]
+    self.assertEqual(list(stdout_queue.queue), expected_output)
+    self.assertEqual(self.gsutil.history, [])
+
+  def test_download_worker_skips_not_found_file(self):
+    sha1_hash = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    input_filename = '%s/%s' % (self.base_url, sha1_hash)
+    output_filename = os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt')
+    self.queue.put((sha1_hash, output_filename))
+    self.queue.put((None, None))
+    stdout_queue = Queue.Queue()
+    self.gsutil.add_expected(1, '', '')  # Return error when 'ls' is called.
+    download_from_google_storage._downloader_worker_thread(
+        0, self.queue, False, self.base_url, self.gsutil,
+        stdout_queue, self.ret_codes)
+    expected_output = [
+        '0> File %s for %s does not exist, skipping.' % (
+            input_filename, output_filename),
+    ]
+    expected_calls = [
+        ('check_call',
+            ('ls', input_filename))
+    ]
+    expected_ret_codes = [
+        (1, 'File %s for %s does not exist.' % (
+            input_filename, output_filename))
+    ]
+    self.assertEqual(list(stdout_queue.queue), expected_output)
+    self.assertEqual(self.gsutil.history, expected_calls)
+    self.assertEqual(list(self.ret_codes.queue), expected_ret_codes)
+
+  def test_download_cp_fails(self):
+    sha1_hash = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    input_filename = '%s/%s' % (self.base_url, sha1_hash)
+    output_filename = os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt')
+    self.gsutil.add_expected(0, '', '')
+    self.gsutil.add_expected(101, '', 'Test error message.')
+    code = download_from_google_storage.download_from_google_storage(
+        input_filename=sha1_hash,
+        base_url=self.base_url,
+        gsutil=self.gsutil,
+        num_threads=1,
+        directory=False,
+        recursive=False,
+        force=True,
+        output=output_filename,
+        ignore_errors=False,
+        sha1_file=False)
+    expected_calls = [
+        ('check_call',
+            ('ls', input_filename)),
+        ('check_call',
+            ('cp', '-q', input_filename, output_filename))
+    ]
+    self.assertEqual(self.gsutil.history, expected_calls)
+    self.assertEqual(code, 101)
+
+  def test_download_directory_no_recursive_non_force(self):
+    sha1_hash = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    input_filename = '%s/%s' % (self.base_url, sha1_hash)
+    output_filename = os.path.join(self.base_path, 'uploaded_lorem_ipsum.txt')
+    code = download_from_google_storage.download_from_google_storage(
+        input_filename=self.base_path,
+        base_url=self.base_url,
+        gsutil=self.gsutil,
+        num_threads=1,
+        directory=True,
+        recursive=False,
+        force=False,
+        output=None,
+        ignore_errors=False,
+        sha1_file=False)
+    expected_calls = [
+        ('check_call',
+            ('ls', input_filename)),
+        ('check_call',
+            ('cp', '-q', input_filename, output_filename))]
+    self.assertEqual(self.gsutil.history, expected_calls)
+    self.assertEqual(code, 0)
+
+
+if __name__ == '__main__':
+  unittest.main()
\ No newline at end of file
diff --git a/tests/gstools/download_test_data/rootfolder_text.txt b/tests/gstools/download_test_data/rootfolder_text.txt
new file mode 100644
index 000000000..6de7b8c69
--- /dev/null
+++ b/tests/gstools/download_test_data/rootfolder_text.txt
@@ -0,0 +1 @@
+This is a test file.
diff --git a/tests/gstools/download_test_data/rootfolder_text.txt.sha1 b/tests/gstools/download_test_data/rootfolder_text.txt.sha1
new file mode 100644
index 000000000..212aed339
--- /dev/null
+++ b/tests/gstools/download_test_data/rootfolder_text.txt.sha1
@@ -0,0 +1 @@
+e6c4fbd4fe7607f3e6ebf68b2ea4ef694da7b4fe
diff --git a/tests/gstools/download_test_data/subfolder/subfolder_text.txt b/tests/gstools/download_test_data/subfolder/subfolder_text.txt
new file mode 100644
index 000000000..27ea4400c
--- /dev/null
+++ b/tests/gstools/download_test_data/subfolder/subfolder_text.txt
@@ -0,0 +1,2 @@
+This is a test file.
+This file exists in a subfolder
diff --git a/tests/gstools/download_test_data/subfolder/subfolder_text.txt.sha1 b/tests/gstools/download_test_data/subfolder/subfolder_text.txt.sha1
new file mode 100644
index 000000000..096b6feb8
--- /dev/null
+++ b/tests/gstools/download_test_data/subfolder/subfolder_text.txt.sha1
@@ -0,0 +1 @@
+b5415aa0b64006a95c0c409182e628881d6d6463
diff --git a/tests/gstools/download_test_data/uploaded_lorem_ipsum.txt.sha1 b/tests/gstools/download_test_data/uploaded_lorem_ipsum.txt.sha1
new file mode 100644
index 000000000..9723fef71
--- /dev/null
+++ b/tests/gstools/download_test_data/uploaded_lorem_ipsum.txt.sha1
@@ -0,0 +1 @@
+7871c8e24da15bad8b0be2c36edc9dc77e37727f
diff --git a/tests/gstools/lorem_ipsum.txt b/tests/gstools/lorem_ipsum.txt
new file mode 100644
index 000000000..0dc0fba09
--- /dev/null
+++ b/tests/gstools/lorem_ipsum.txt
@@ -0,0 +1,6 @@
+Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
+tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
+quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
+consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
+cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
+proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
diff --git a/tests/gstools/lorem_ipsum.txt.md5 b/tests/gstools/lorem_ipsum.txt.md5
new file mode 100644
index 000000000..3aede178d
--- /dev/null
+++ b/tests/gstools/lorem_ipsum.txt.md5
@@ -0,0 +1 @@
+734d7c1ed3545383837428f031840a1e
diff --git a/tests/gstools/lorem_ipsum2.txt b/tests/gstools/lorem_ipsum2.txt
new file mode 100644
index 000000000..76da195ab
--- /dev/null
+++ b/tests/gstools/lorem_ipsum2.txt
@@ -0,0 +1,7 @@
+Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
+tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
+quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
+consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
+cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
+proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
+This is the second file.
diff --git a/tests/upload_to_google_storage_unittests.py b/tests/upload_to_google_storage_unittests.py
new file mode 100755
index 000000000..8879f5cf8
--- /dev/null
+++ b/tests/upload_to_google_storage_unittests.py
@@ -0,0 +1,165 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Unit tests for upload_to_google_storage.py."""
+
+import optparse
+import os
+import Queue
+import shutil
+import StringIO
+import sys
+import tempfile
+import threading
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+import upload_to_google_storage
+from download_from_google_storage_unittests import GsutilMock
+
+# ../third_party/gsutil/gsutil
+GSUTIL_DEFAULT_PATH = os.path.join(
+    os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
+    'third_party', 'gsutil', 'gsutil')
+TEST_DIR = os.path.dirname(os.path.abspath(__file__))
+
+
+class UploadTests(unittest.TestCase):
+  def setUp(self):
+    self.gsutil = GsutilMock(GSUTIL_DEFAULT_PATH)
+    self.temp_dir = tempfile.mkdtemp(prefix='gstools_test')
+    self.base_path = os.path.join(self.temp_dir, 'gstools')
+    shutil.copytree(os.path.join(TEST_DIR, 'gstools'), self.base_path)
+    self.base_url = 'gs://sometesturl'
+    self.parser = optparse.OptionParser()
+    self.ret_codes = Queue.Queue()
+    self.stdout_queue = Queue.Queue()
+    self.lorem_ipsum = os.path.join(self.base_path, 'lorem_ipsum.txt')
+    self.lorem_ipsum_sha1 = '7871c8e24da15bad8b0be2c36edc9dc77e37727f'
+
+  def cleanUp(self):
+    shutil.rmtree(self.temp_dir)
+    sys.stdin = sys.__stdin__
+
+  def test_upload_single_file(self):
+    filenames = [self.lorem_ipsum]
+    output_filename = '%s.sha1'  % self.lorem_ipsum
+    code = upload_to_google_storage.upload_to_google_storage(
+        filenames, self.base_url, self.gsutil, True, False, 1, False)
+    self.assertEqual(
+        self.gsutil.history,
+        [('check_call',
+          ('ls', '%s/%s' % (self.base_url, self.lorem_ipsum_sha1))),
+         ('check_call',
+          ('cp', '-q', filenames[0], '%s/%s' % (self.base_url,
+                                                self.lorem_ipsum_sha1)))])
+    self.assertTrue(os.path.exists(output_filename))
+    self.assertEqual(
+        open(output_filename, 'rb').read(),
+        '7871c8e24da15bad8b0be2c36edc9dc77e37727f')
+    os.remove(output_filename)
+    self.assertEqual(code, 0)
+
+  def test_upload_single_file_remote_exists(self):
+    filenames = [self.lorem_ipsum]
+    output_filename = '%s.sha1'  % self.lorem_ipsum
+    etag_string = 'ETag: 634d7c1ed3545383837428f031840a1e'
+    self.gsutil.add_expected(0, '', '')
+    self.gsutil.add_expected(0, etag_string, '')
+    code = upload_to_google_storage.upload_to_google_storage(
+        filenames, self.base_url, self.gsutil, False, False, 1, False)
+    self.assertEqual(
+        self.gsutil.history,
+        [('check_call',
+          ('ls', '%s/%s' % (self.base_url, self.lorem_ipsum_sha1))),
+         ('check_call',
+          ('ls', '-L', '%s/%s' % (self.base_url, self.lorem_ipsum_sha1)))])
+    self.assertTrue(os.path.exists(output_filename))
+    self.assertEqual(
+        open(output_filename, 'rb').read(),
+        '7871c8e24da15bad8b0be2c36edc9dc77e37727f')
+    os.remove(output_filename)
+    self.assertEqual(code, 0)
+
+  def test_upload_worker_errors(self):
+    work_queue = Queue.Queue()
+    work_queue.put((self.lorem_ipsum, self.lorem_ipsum_sha1))
+    work_queue.put((None, None))
+    self.gsutil.add_expected(1, '', '')  # For the first ls call.
+    self.gsutil.add_expected(20, '', 'Expected error message')
+    # pylint: disable=W0212
+    upload_to_google_storage._upload_worker(
+        0,
+        work_queue,
+        self.base_url,
+        self.gsutil,
+        threading.Lock(),
+        False,
+        False,
+        self.stdout_queue,
+        self.ret_codes)
+    expected_ret_codes = [
+      (20,
+       'Encountered error on uploading %s to %s/%s\nExpected error message' %
+          (self.lorem_ipsum, self.base_url, self.lorem_ipsum_sha1))]
+    self.assertEqual(list(self.ret_codes.queue), expected_ret_codes)
+
+  def test_skip_hashing(self):
+    filenames = [self.lorem_ipsum]
+    output_filename = '%s.sha1' % self.lorem_ipsum
+    fake_hash = '6871c8e24da15bad8b0be2c36edc9dc77e37727f'
+    with open(output_filename, 'wb') as f:
+      f.write(fake_hash)  # Fake hash.
+    code = upload_to_google_storage.upload_to_google_storage(
+        filenames, self.base_url, self.gsutil, False, False, 1, True)
+    self.assertEqual(
+        self.gsutil.history,
+        [('check_call',
+          ('ls', '%s/%s' % (self.base_url, fake_hash))),
+         ('check_call',
+          ('ls', '-L', '%s/%s' % (self.base_url, fake_hash))),
+         ('check_call',
+          ('cp', '-q', filenames[0], '%s/%s' % (self.base_url, fake_hash)))])
+    self.assertEqual(
+        open(output_filename, 'rb').read(), fake_hash)
+    os.remove(output_filename)
+    self.assertEqual(code, 0)
+
+  def test_get_targets_no_args(self):
+    try:
+      upload_to_google_storage.get_targets([], self.parser, False)
+      self.fail()
+    except SystemExit, e:
+      self.assertEqual(e.code, 2)
+
+  def test_get_targets_passthrough(self):
+    result = upload_to_google_storage.get_targets(
+        ['a', 'b', 'c', 'd', 'e'],
+        self.parser,
+        False)
+    self.assertEqual(result, ['a', 'b', 'c', 'd', 'e'])
+
+  def test_get_targets_multiple_stdin(self):
+    inputs = ['a', 'b', 'c', 'd', 'e']
+    sys.stdin = StringIO.StringIO(os.linesep.join(inputs))
+    result = upload_to_google_storage.get_targets(
+        ['-'],
+        self.parser,
+        False)
+    self.assertEqual(result, inputs)
+
+  def test_get_targets_multiple_stdin_null(self):
+    inputs = ['a', 'b', 'c', 'd', 'e']
+    sys.stdin = StringIO.StringIO('\0'.join(inputs))
+    result = upload_to_google_storage.get_targets(
+        ['-'],
+        self.parser,
+        True)
+    self.assertEqual(result, inputs)
+
+
+if __name__ == '__main__':
+  unittest.main()
\ No newline at end of file
diff --git a/upload_to_google_storage.py b/upload_to_google_storage.py
new file mode 100755
index 000000000..5ff85c781
--- /dev/null
+++ b/upload_to_google_storage.py
@@ -0,0 +1,245 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Uploads files to Google Storage content addressed."""
+
+import hashlib
+import optparse
+import os
+import Queue
+import re
+import sys
+import threading
+import time
+
+from download_from_google_storage import check_bucket_permissions
+from download_from_google_storage import get_sha1
+from download_from_google_storage import Gsutil
+from download_from_google_storage import printer_worker
+
+GSUTIL_DEFAULT_PATH = os.path.join(
+    os.path.dirname(os.path.abspath(__file__)),
+    'third_party', 'gsutil', 'gsutil')
+
+USAGE_STRING = """%prog [options] target [target2 ...].
+Target is the file intended to be uploaded to Google Storage.
+If target is "-", then a list of files will be taken from standard input
+
+This script will generate a file (original filename).sha1 containing the
+sha1 sum of the uploaded file.
+It is recommended that the .sha1 file is checked into the repository,
+the original file removed from the repository, and a hook added to the
+DEPS file to call download_from_google_storage.py.
+
+Example usages
+--------------
+
+Scan the current directory and upload all files larger than 1MB:
+find . -name .svn -prune -o -size +1000k -type f -print0 | %prog -0 -b bkt -
+(Replace "bkt" with the name of a writable bucket.)
+"""
+
+
+def get_md5(filename):
+  md5_calculator = hashlib.md5()
+  with open(filename, 'rb') as f:
+    while True:
+      chunk = f.read(1024*1024)
+      if not chunk:
+        break
+      md5_calculator.update(chunk)
+  return md5_calculator.hexdigest()
+
+
+def get_md5_cached(filename):
+  """Don't calculate the MD5 if we can find a .md5 file."""
+  # See if we can find an existing MD5 sum stored in a file.
+  if os.path.exists('%s.md5' % filename):
+    with open('%s.md5' % filename, 'rb') as f:
+      md5_match = re.search('([a-z0-9]{32})', f.read())
+      if md5_match:
+        return md5_match.group(1)
+  else:
+    md5_hash = get_md5(filename)
+    with open('%s.md5' % filename, 'wb') as f:
+      f.write(md5_hash)
+    return md5_hash
+
+
+def _upload_worker(
+    thread_num, upload_queue, base_url, gsutil, md5_lock, force,
+    use_md5, stdout_queue, ret_codes):
+  while True:
+    filename, sha1_sum = upload_queue.get()
+    if not filename:
+      break
+    file_url = '%s/%s' % (base_url, sha1_sum)
+    if gsutil.check_call('ls', file_url)[0] == 0 and not force:
+      # File exists, check MD5 hash.
+      _, out, _ = gsutil.check_call('ls', '-L', file_url)
+      etag_match = re.search('ETag:\s+([a-z0-9]{32})', out)
+      if etag_match:
+        remote_md5 = etag_match.group(1)
+        # Calculate the MD5 checksum to match it to Google Storage's ETag.
+        with md5_lock:
+          if use_md5:
+            local_md5 = get_md5_cached(filename)
+          else:
+            local_md5 = get_md5(filename)
+        if local_md5 == remote_md5:
+          stdout_queue.put(
+              '%d> File %s already exists and MD5 matches, upload skipped' %
+              (thread_num, filename))
+          continue
+    stdout_queue.put('%d> Uploading %s...' % (
+        thread_num, filename))
+    code, _, err = gsutil.check_call('cp', '-q', filename, file_url)
+    if code != 0:
+      ret_codes.put(
+          (code,
+           'Encountered error on uploading %s to %s\n%s' %
+           (filename, file_url, err)))
+      continue
+
+
+def get_targets(args, parser, use_null_terminator):
+  if not args:
+    parser.error('Missing target.')
+
+  if len(args) == 1 and args[0] == '-':
+    # Take stdin as a newline or null seperated list of files.
+    if use_null_terminator:
+      return sys.stdin.read().split('\0')
+    else:
+      return sys.stdin.read().splitlines()
+  else:
+    return args
+
+
+def upload_to_google_storage(
+    input_filenames, base_url, gsutil, force,
+    use_md5, num_threads, skip_hashing):
+  # We only want one MD5 calculation happening at a time to avoid HD thrashing.
+  md5_lock = threading.Lock()
+
+  # Start up all the worker threads plus the printer thread.
+  all_threads = []
+  ret_codes = Queue.Queue()
+  ret_codes.put((0, None))
+  upload_queue = Queue.Queue()
+  upload_timer = time.time()
+  stdout_queue = Queue.Queue()
+  printer_thread = threading.Thread(target=printer_worker, args=[stdout_queue])
+  printer_thread.daemon = True
+  printer_thread.start()
+  for thread_num in range(num_threads):
+    t = threading.Thread(
+        target=_upload_worker,
+        args=[thread_num, upload_queue, base_url, gsutil, md5_lock,
+              force, use_md5, stdout_queue, ret_codes])
+    t.daemon = True
+    t.start()
+    all_threads.append(t)
+
+  # We want to hash everything in a single thread since its faster.
+  # The bottleneck is in disk IO, not CPU.
+  hashing_start = time.time()
+  for filename in input_filenames:
+    if not os.path.exists(filename):
+      stdout_queue.put('Main> Error: %s not found, skipping.' % filename)
+      continue
+    if os.path.exists('%s.sha1' % filename) and skip_hashing:
+      stdout_queue.put(
+          'Main> Found hash for %s, sha1 calculation skipped.' % filename)
+      with open(filename + '.sha1', 'rb') as f:
+        sha1_file = f.read(1024)
+      if not re.match('^([a-z0-9]{40})$', sha1_file):
+        print >> sys.stderr, 'Invalid sha1 hash file %s.sha1' % filename
+        return 1
+      upload_queue.put((filename, sha1_file))
+      continue
+    stdout_queue.put('Main> Calculating hash for %s...' % filename)
+    sha1_sum = get_sha1(filename)
+    with open(filename + '.sha1', 'wb') as f:
+      f.write(sha1_sum)
+    stdout_queue.put('Main> Done calculating hash for %s.' % filename)
+    upload_queue.put((filename, sha1_sum))
+  hashing_duration = time.time() - hashing_start
+
+  # Wait for everything to finish.
+  for _ in all_threads:
+    upload_queue.put((None, None))  # To mark the end of the work queue.
+  for t in all_threads:
+    t.join()
+  stdout_queue.put(None)
+  printer_thread.join()
+
+  # Print timing information.
+  print 'Hashing %s files took %1f seconds' % (
+      len(input_filenames), hashing_duration)
+  print 'Uploading took %1f seconds' % (time.time() - upload_timer)
+
+  # See if we ran into any errors.
+  max_ret_code = 0
+  for ret_code, message in ret_codes.queue:
+    max_ret_code = max(ret_code, max_ret_code)
+    if message:
+      print >> sys.stderr, message
+
+  if not max_ret_code:
+    print 'Success!'
+
+  return max_ret_code
+
+
+def main(args):
+  parser = optparse.OptionParser(USAGE_STRING)
+  parser.add_option('-b', '--bucket',
+                    help='Google Storage bucket to upload to.')
+  parser.add_option('-e', '--boto', help='Specify a custom boto file.')
+  parser.add_option('-f', '--force', action='store_true',
+                    help='Force upload even if remote file exists.')
+  parser.add_option('-g', '--gsutil_path', default=GSUTIL_DEFAULT_PATH,
+                    help='Path to the gsutil script.')
+  parser.add_option('-m', '--use_md5', action='store_true',
+                    help='Generate MD5 files when scanning, and don\'t check '
+                    'the MD5 checksum if a .md5 file is found.')
+  parser.add_option('-t', '--num_threads', default=1, type='int',
+                    help='Number of uploader threads to run.')
+  parser.add_option('-s', '--skip_hashing', action='store_true',
+                    help='Skip hashing if .sha1 file exists.')
+  parser.add_option('-0', '--use_null_terminator', action='store_true',
+                    help='Use \\0 instead of \\n when parsing '
+                    'the file list from stdin.  This is useful if the input '
+                    'is coming from "find ... -print0".')
+  (options, args) = parser.parse_args()
+
+  # Enumerate our inputs.
+  input_filenames = get_targets(args, parser, options.use_null_terminator)
+
+  # Make sure we can find a working instance of gsutil.
+  if os.path.exists(GSUTIL_DEFAULT_PATH):
+    gsutil = Gsutil(GSUTIL_DEFAULT_PATH)
+  else:
+    gsutil = None
+    for path in os.environ["PATH"].split(os.pathsep):
+      if os.path.exists(path) and 'gsutil' in os.listdir(path):
+        gsutil = Gsutil(os.path.join(path, 'gsutil'))
+    if not gsutil:
+      parser.error('gsutil not found in %s, bad depot_tools checkout?' %
+                   GSUTIL_DEFAULT_PATH)
+
+  # Check we have a valid bucket with valid permissions.
+  base_url, code = check_bucket_permissions(options.bucket, gsutil)
+  if code:
+    return code
+
+  return upload_to_google_storage(
+      input_filenames, base_url, gsutil, options.force, options.use_md5,
+      options.num_threads, options.skip_hashing)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))
\ No newline at end of file