diff --git a/.gitignore b/.gitignore
index 4144e3695..4f6bf5e84 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,6 +24,8 @@
 /git_bin
 /git-1.8.0_bin
 /svn_bin
+/win_toolchain/vs2013_files
+/win_toolchain/.timestamps
 
 # Ignore ctags/cscope index files
 /TAGS
diff --git a/update_depot_tools.bat b/update_depot_tools.bat
index 58d3d8497..d461aab64 100644
--- a/update_depot_tools.bat
+++ b/update_depot_tools.bat
@@ -30,6 +30,13 @@ if errorlevel 1 goto :EOF
 :: Now clear errorlevel so it can be set by other programs later.
 set errorlevel=
 
+:: Opt-in for now.
+IF "%DEPOT_TOOLS_WIN_TOOLCHAIN%" == "" GOTO :NOTOOLCHAIN
+call python %~dp0win_toolchain\get_toolchain_if_necessary.py
+if errorlevel 1 goto :EOF
+set errorlevel=
+:NOTOOLCHAIN
+
 :: Shall skip automatic update?
 IF "%DEPOT_TOOLS_UPDATE%" == "0" GOTO :EOF
 
diff --git a/win_toolchain/7z/7z.dll b/win_toolchain/7z/7z.dll
new file mode 100644
index 000000000..cea996e4f
Binary files /dev/null and b/win_toolchain/7z/7z.dll differ
diff --git a/win_toolchain/7z/7z.exe b/win_toolchain/7z/7z.exe
new file mode 100644
index 000000000..b55fefe6d
Binary files /dev/null and b/win_toolchain/7z/7z.exe differ
diff --git a/win_toolchain/7z/LICENSE b/win_toolchain/7z/LICENSE
new file mode 100644
index 000000000..21bb84e78
--- /dev/null
+++ b/win_toolchain/7z/LICENSE
@@ -0,0 +1,57 @@
+  7-Zip
+  ~~~~~
+  License for use and distribution
+  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+  7-Zip Copyright (C) 1999-2012 Igor Pavlov.
+
+  Licenses for files are:
+
+    1) 7z.dll: GNU LGPL + unRAR restriction
+    2) All other files:  GNU LGPL
+
+  The GNU LGPL + unRAR restriction means that you must follow both 
+  GNU LGPL rules and unRAR restriction rules.
+
+
+  Note: 
+    You can use 7-Zip on any computer, including a computer in a commercial 
+    organization. You don't need to register or pay for 7-Zip.
+
+
+  GNU LGPL information
+  --------------------
+
+    This library is free software; you can redistribute it and/or
+    modify it under the terms of the GNU Lesser General Public
+    License as published by the Free Software Foundation; either
+    version 2.1 of the License, or (at your option) any later version.
+
+    This library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+    Lesser General Public License for more details.
+
+    You can receive a copy of the GNU Lesser General Public License from 
+    http://www.gnu.org/
+
+
+  unRAR restriction
+  -----------------
+
+    The decompression engine for RAR archives was developed using source 
+    code of unRAR program.
+    All copyrights to original unRAR code are owned by Alexander Roshal.
+
+    The license for original unRAR code has the following restriction:
+
+      The unRAR sources cannot be used to re-create the RAR compression algorithm, 
+      which is proprietary. Distribution of modified unRAR sources in separate form 
+      or as a part of other software is permitted, provided that it is clearly
+      stated in the documentation and source comments that the code may
+      not be used to develop a RAR (WinRAR) compatible archiver.
+
+
+  --
+  Igor Pavlov
+
diff --git a/win_toolchain/get_toolchain_if_necessary.py b/win_toolchain/get_toolchain_if_necessary.py
new file mode 100755
index 000000000..ecced5fe1
--- /dev/null
+++ b/win_toolchain/get_toolchain_if_necessary.py
@@ -0,0 +1,163 @@
+#!/usr/bin/env python
+# Copyright 2013 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.
+
+"""Downloads and unpacks a toolchain for building on Windows. The contents are
+matched by sha1 which will be updated when the toolchain is updated.
+
+Having a toolchain script in depot_tools means that it's not versioned
+directly with the source code. That is, if the toolchain is upgraded, but
+you're trying to build an historical version of Chromium from before the
+toolchain upgrade, this will cause you to build with a newer toolchain than
+was available when that code was committed. This is done for a two main
+reasons: 1) it would likely be annoying to have the up-to-date toolchain
+removed and replaced by one without a service pack applied); 2) it would
+require maintaining scripts that can build older not-up-to-date revisions of
+the toolchain. This is likely to be a poorly tested code path that probably
+won't be properly maintained. See http://crbug.com/323300.
+
+This does not extend to major versions of the toolchain however, on the
+assumption that there are more likely to be source incompatibilities between
+major revisions. This script calls a subscript (currently, toolchain2013.py)
+to do the main work. It is expected that toolchain2013.py will always be able
+to acquire/build the most current revision of a VS2013-based toolchain. In the
+future when a hypothetical VS2015 is released, the 2013 script will be
+maintained, and a new 2015 script would be added.
+"""
+
+import ctypes.wintypes
+import hashlib
+import json
+import os
+import subprocess
+import sys
+
+
+BASEDIR = os.path.dirname(os.path.abspath(__file__))
+
+
+GetFileAttributes = ctypes.windll.kernel32.GetFileAttributesW
+GetFileAttributes.argtypes = (ctypes.wintypes.LPWSTR,)
+GetFileAttributes.restype = ctypes.wintypes.DWORD
+FILE_ATTRIBUTE_HIDDEN = 0x2
+FILE_ATTRIBUTE_SYSTEM = 0x4
+
+
+def IsHidden(file_path):
+  """Returns whether the given |file_path| has the 'system' or 'hidden'
+  attribute set."""
+  p = GetFileAttributes(file_path)
+  assert p != 0xffffffff
+  return bool(p & (FILE_ATTRIBUTE_HIDDEN | FILE_ATTRIBUTE_SYSTEM))
+
+
+def GetFileList(root):
+  """Gets a normalized list of files under |root|."""
+  assert not os.path.isabs(root)
+  assert os.path.normpath(root) == root
+  file_list = []
+  for base, _, files in os.walk(root):
+    paths = [os.path.join(base, f) for f in files]
+    file_list.extend(x.lower() for x in paths if not IsHidden(x))
+  return sorted(file_list)
+
+
+def MakeTimestampsFileName(root):
+  return os.path.join(root, '..', '.timestamps')
+
+
+def CalculateHash(root):
+  """Calculates the sha1 of the paths to all files in the given |root| and the
+  contents of those files, and returns as a hex string."""
+  file_list = GetFileList(root)
+
+  # Check whether we previously saved timestamps in $root/../.timestamps. If
+  # we didn't, or they don't match, then do the full calculation, otherwise
+  # return the saved value.
+  timestamps_file = MakeTimestampsFileName(root)
+  timestamps_data = {'files': [], 'sha1': ''}
+  if os.path.exists(timestamps_file):
+    with open(timestamps_file, 'rb') as f:
+      try:
+        timestamps_data = json.load(f)
+      except ValueError:
+        # json couldn't be loaded, empty data will force a re-hash.
+        pass
+
+  matches = len(file_list) == len(timestamps_data['files'])
+  if matches:
+    for disk, cached in zip(file_list, timestamps_data['files']):
+      if disk != cached[0] or os.stat(disk).st_mtime != cached[1]:
+        matches = False
+        break
+  if matches:
+    return timestamps_data['sha1']
+
+  digest = hashlib.sha1()
+  for path in file_list:
+    digest.update(path)
+    with open(path, 'rb') as f:
+      digest.update(f.read())
+  return digest.hexdigest()
+
+
+def SaveTimestampsAndHash(root, sha1):
+  """Save timestamps and the final hash to be able to early-out more quickly
+  next time."""
+  file_list = GetFileList(root)
+  timestamps_data = {
+    'files': [[f, os.stat(f).st_mtime] for f in file_list],
+    'sha1': sha1,
+  }
+  with open(MakeTimestampsFileName(root), 'wb') as f:
+    json.dump(timestamps_data, f)
+
+
+def main():
+  if not sys.platform.startswith(('cygwin', 'win32')):
+    return 0
+
+  if len(sys.argv) != 1:
+    print >> sys.stderr, 'Unexpected arguments.'
+    return 1
+
+  # Move to depot_tools\win_toolchain where we'll store our files, and where
+  # the downloader script is.
+  os.chdir(os.path.normpath(os.path.join(BASEDIR)))
+  toolchain_dir = '.'
+  target_dir = os.path.normpath(os.path.join(toolchain_dir, 'vs2013_files'))
+
+  sha1path = os.path.join(toolchain_dir, 'toolchain_vs2013.hash')
+  desired_hash = ''
+  if os.path.isfile(sha1path):
+    with open(sha1path, 'rb') as f:
+      desired_hash = f.read().strip()
+
+  # If the current hash doesn't match what we want in the file, nuke and pave.
+  # Typically this script is only run when the .sha1 one file is updated, but
+  # directly calling "gclient runhooks" will also run it, so we cache
+  # based on timestamps to make that case fast.
+  current_hash = CalculateHash(target_dir)
+  if current_hash != desired_hash:
+    print 'Windows toolchain out of date or doesn\'t exist, updating...'
+    if os.path.isdir(target_dir):
+      subprocess.check_call('rmdir /s/q "%s"' % target_dir, shell=True)
+    subprocess.check_call([
+        sys.executable,
+        'toolchain2013.py',
+        '--targetdir', target_dir])
+    current_hash = CalculateHash(target_dir)
+    if current_hash != desired_hash:
+      print >> sys.stderr, (
+          'Got wrong hash after pulling a new toolchain. '
+          'Wanted \'%s\', got \'%s\'.' % (
+              desired_hash, current_hash))
+      return 1
+    SaveTimestampsAndHash(target_dir, current_hash)
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())
diff --git a/win_toolchain/toolchain2013.py b/win_toolchain/toolchain2013.py
new file mode 100755
index 000000000..2bce633a2
--- /dev/null
+++ b/win_toolchain/toolchain2013.py
@@ -0,0 +1,290 @@
+#!/usr/bin/env python
+# Copyright 2013 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.
+
+"""Extracts a Windows VS2013 toolchain from various downloadable pieces."""
+
+
+import ctypes
+import optparse
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import urllib2
+
+
+BASEDIR = os.path.dirname(os.path.abspath(__file__))
+g_temp_dirs = []
+
+
+def GetLongPathName(path):
+  """Converts any 8dot3 names in the path to the full name."""
+  buf = ctypes.create_unicode_buffer(260)
+  size = ctypes.windll.kernel32.GetLongPathNameW(unicode(path), buf, 260)
+  if (size > 260):
+    sys.exit('Long form of path longer than 260 chars: %s' % path)
+  return buf.value
+
+
+def RunOrDie(command):
+  subprocess.check_call(command, shell=True)
+
+
+def TempDir():
+  """Generates a temporary directory (for downloading or extracting to) and keep
+  track of the directory that's created for cleaning up later.
+  """
+  global g_temp_dirs
+  temp = tempfile.mkdtemp()
+  g_temp_dirs.append(temp)
+  return temp
+
+
+def DeleteAllTempDirs():
+  """Removes all temporary directories created by |TempDir()|."""
+  global g_temp_dirs
+  if g_temp_dirs:
+    sys.stdout.write('Cleaning up temporaries...\n')
+  for temp in g_temp_dirs:
+    # shutil.rmtree errors out on read only attributes.
+    RunOrDie('rmdir /s/q "%s"' % temp)
+  g_temp_dirs = []
+
+
+def GetIsoUrl(pro):
+  """Gets the .iso URL.
+
+  If |pro| is False, downloads the Express edition.
+  """
+  prefix = 'http://download.microsoft.com/download/'
+  if pro:
+    return (prefix +
+        'A/F/1/AF128362-A6A8-4DB3-A39A-C348086472CC/VS2013_RTM_PRO_ENU.iso')
+  else:
+    return (prefix +
+        '7/2/E/72E0F986-D247-4289-B9DC-C4FB07374894/VS2013_RTM_DskExp_ENU.iso')
+
+
+def Download(url, local_path):
+  """Downloads a large-ish binary file and print some status information while
+  doing so.
+  """
+  sys.stdout.write('Downloading %s...\n' % url)
+  req = urllib2.urlopen(url)
+  content_length = int(req.headers.get('Content-Length', 0))
+  bytes_read = 0L
+  terminator = '\r' if sys.stdout.isatty() else '\n'
+  with open(local_path, 'wb') as file:
+    while True:
+      chunk = req.read(1024 * 1024)
+      if not chunk:
+        break
+      bytes_read += len(chunk)
+      file.write(chunk)
+      sys.stdout.write('... %d/%d%s' % (bytes_read, content_length, terminator))
+      sys.stdout.flush()
+  sys.stdout.write('\n')
+  if content_length and content_length != bytes_read:
+    raise SystemExit('Got incorrect number of bytes downloading %s' % url)
+
+
+def ExtractIso(iso_path):
+  """Uses 7zip to extract the contents of the given .iso (or self-extracting
+  .exe).
+  """
+  target_path = TempDir()
+  sys.stdout.write('Extracting %s...\n' % iso_path)
+  sys.stdout.flush()
+  # TODO(scottmg): Do this (and exe) manually with python code.
+  # Note that at the beginning of main() we set the working directory to 7z's
+  # location so that 7z can find its codec dll.
+  RunOrDie('7z x "%s" -y "-o%s" >nul' % (iso_path, target_path))
+  return target_path
+
+
+def ExtractMsi(msi_path):
+  """Uses msiexec to extract the contents of the given .msi file."""
+  sys.stdout.write('Extracting %s...\n' % msi_path)
+  target_path = TempDir()
+  RunOrDie('msiexec /a "%s" /qn TARGETDIR="%s"' % (msi_path, target_path))
+  return target_path
+
+
+def DownloadMainIso(url):
+  temp_dir = TempDir()
+  target_path = os.path.join(temp_dir, os.path.basename(url))
+  Download(url, target_path)
+  return target_path
+
+
+def GetSourceImage(local_dir, pro):
+  url = GetIsoUrl(pro)
+  if local_dir:
+    return os.path.join(local_dir, os.path.basename(url))
+  else:
+    return DownloadMainIso(url)
+
+
+def ExtractMsiList(iso_dir, packages):
+  """Extracts the contents of a list of .msi files from an already extracted
+  .iso file.
+
+  |packages| is a list of pairs (msi, required). If required is not True, the
+  msi is optional (this is set for packages that are in Pro but not Express).
+  """
+  results = []
+  for (package, required) in packages:
+    path_to_package = os.path.join(iso_dir, 'packages', package)
+    if not os.path.exists(path_to_package) and not required:
+      continue
+    results.append(ExtractMsi(path_to_package))
+  return results
+
+
+def ExtractComponents(image):
+  packages = [
+      (r'vcRuntimeAdditional_amd64\vc_runtimeAdditional_x64.msi', True),
+      (r'vcRuntimeAdditional_x86\vc_runtimeAdditional_x86.msi', True),
+      (r'vcRuntimeDebug_amd64\vc_runtimeDebug_x64.msi', True),
+      (r'vcRuntimeDebug_x86\vc_runtimeDebug_x86.msi', True),
+      (r'vcRuntimeMinimum_amd64\vc_runtimeMinimum_x64.msi', True),
+      (r'vcRuntimeMinimum_x86\vc_runtimeMinimum_x86.msi', True),
+      (r'vc_compilerCore86\vc_compilerCore86.msi', True),
+      (r'vc_compilerCore86res\vc_compilerCore86res.msi', True),
+      (r'vc_compilerx64nat\vc_compilerx64nat.msi', False),
+      (r'vc_compilerx64natres\vc_compilerx64natres.msi', False),
+      (r'vc_compilerx64x86\vc_compilerx64x86.msi', False),
+      (r'vc_compilerx64x86res\vc_compilerx64x86res.msi', False),
+      (r'vc_librarycore86\vc_librarycore86.msi', True),
+      (r'vc_libraryDesktop\x64\vc_LibraryDesktopX64.msi', True),
+      (r'vc_libraryDesktop\x86\vc_LibraryDesktopX86.msi', True),
+      (r'vc_libraryextended\vc_libraryextended.msi', False),
+      (r'Windows_SDK\Windows Software Development Kit-x86_en-us.msi', True),
+      ('Windows_SDK\\'
+       r'Windows Software Development Kit for Metro style Apps-x86_en-us.msi',
+          True),
+    ]
+  extracted_iso = ExtractIso(image)
+  return ExtractMsiList(extracted_iso, packages)
+
+
+def CopyToFinalLocation(extracted_dirs, target_dir):
+  sys.stdout.write('Copying to final location...\n')
+  mappings = {
+      'Program Files\\Microsoft Visual Studio 12.0\\': '.\\',
+      'System64\\': 'sys64\\',
+      'System\\': 'sys32\\',
+      'Windows Kits\\8.0\\': 'win8sdk\\',
+  }
+  matches = []
+  for extracted_dir in extracted_dirs:
+    for root, dirnames, filenames in os.walk(extracted_dir):
+      for filename in filenames:
+        matches.append((extracted_dir, os.path.join(root, filename)))
+
+  copies = []
+  for prefix, full_path in matches:
+    # +1 for trailing \.
+    partial_path = full_path[len(prefix) + 1:]
+    for map_from, map_to in mappings.iteritems():
+      if partial_path.startswith(map_from):
+        target_path = os.path.join(map_to, partial_path[len(map_from):])
+        copies.append((full_path, os.path.join(target_dir, target_path)))
+
+  for full_source, full_target in copies:
+    target_dir = os.path.dirname(full_target)
+    if not os.path.isdir(target_dir):
+      os.makedirs(target_dir)
+    shutil.copy2(full_source, full_target)
+
+
+def GenerateSetEnvCmd(target_dir, pro):
+  """Generate a batch file that gyp expects to exist to set up the compiler
+  environment.
+
+  This is normally generated by a full install of the SDK, but we
+  do it here manually since we do not do a full install."""
+  with open(os.path.join(
+        target_dir, r'win8sdk\bin\SetEnv.cmd'), 'w') as f:
+    f.write('@echo off\n'
+            ':: Generated by win_toolchain\\toolchain2013.py.\n'
+            # Common to x86 and x64
+            'set PATH=%~dp0..\\..\\Common7\\IDE;%PATH%\n'
+            'set INCLUDE=%~dp0..\\..\\win8sdk\\Include\\um;'
+               '%~dp0..\\..\\win8sdk\\Include\\shared;'
+               '%~dp0..\\..\\VC\\include;'
+               '%~dp0..\\..\\VC\\atlmfc\\include\n'
+            'if "%1"=="/x64" goto x64\n')
+
+    # x86. If we're Pro, then use the amd64_x86 cross (we don't support x86
+    # host at all).
+    if pro:
+      f.write('set PATH=%~dp0..\\..\\win8sdk\\bin\\x86;'
+                '%~dp0..\\..\\VC\\bin\\amd64_x86;'
+                '%~dp0..\\..\\VC\\bin\\amd64;'  # Needed for mspdb120.dll.
+                '%PATH%\n')
+    else:
+      f.write('set PATH=%~dp0..\\..\\win8sdk\\bin\\x86;'
+                '%~dp0..\\..\\VC\\bin;%PATH%\n')
+    f.write('set LIB=%~dp0..\\..\\VC\\lib;'
+               '%~dp0..\\..\\win8sdk\\Lib\\win8\\um\\x86;'
+               '%~dp0..\\..\\VC\\atlmfc\\lib\n'
+            'goto :EOF\n')
+
+    # Express does not include a native 64 bit compiler, so we have to use
+    # the x86->x64 cross.
+    if not pro:
+      # x86->x64 cross.
+      f.write(':x64\n'
+              'set PATH=%~dp0..\\..\\win8sdk\\bin\\x64;'
+                 '%~dp0..\\..\\VC\\bin\\x86_amd64;'
+                 '%PATH%\n')
+    else:
+      # x64 native.
+      f.write(':x64\n'
+              'set PATH=%~dp0..\\..\\win8sdk\\bin\\x64;'
+                 '%~dp0..\\..\\VC\\bin\\amd64;'
+                 '%PATH%\n')
+    f.write('set LIB=%~dp0..\\..\\VC\\lib\\amd64;'
+               '%~dp0..\\..\\win8sdk\\Lib\\win8\\um\\x64;'
+               '%~dp0..\\..\\VC\\atlmfc\\lib\\amd64\n')
+
+
+def main():
+  parser = optparse.OptionParser(description=sys.modules[__name__].__doc__)
+  parser.add_option('--targetdir', metavar='DIR',
+                    help='put toolchain into DIR',
+                    default=os.path.join(BASEDIR, 'win_toolchain_2013'))
+  parser.add_option('--noclean', action='store_false', dest='clean',
+                    help='do not remove temp files',
+                    default=True)
+  parser.add_option('--local', metavar='DIR',
+                    help='use downloaded files from DIR')
+  parser.add_option('--express',
+                    help='use VS Express instead of Pro', action='store_true')
+  options, args = parser.parse_args()
+  try:
+    target_dir = os.path.abspath(options.targetdir)
+    if os.path.exists(target_dir):
+      parser.error('%s already exists. Please [re]move it or use '
+                   '--targetdir to select a different target.\n' %
+                   target_dir)
+    # Set the working directory to 7z subdirectory. 7-zip doesn't find its
+    # codec dll very well, so this is the simplest way to make sure it runs
+    # correctly, as we don't otherwise care about working directory.
+    os.chdir(os.path.join(BASEDIR, '7z'))
+    image = GetSourceImage(options.local, not options.express)
+    extracted = ExtractComponents(image)
+    CopyToFinalLocation(extracted, target_dir)
+
+    GenerateSetEnvCmd(target_dir, not options.express)
+  finally:
+    if options.clean:
+      DeleteAllTempDirs()
+
+
+if __name__ == '__main__':
+  sys.exit(main())
diff --git a/win_toolchain/toolchain_vs2013.hash b/win_toolchain/toolchain_vs2013.hash
new file mode 100644
index 000000000..98dde202f
--- /dev/null
+++ b/win_toolchain/toolchain_vs2013.hash
@@ -0,0 +1 @@
+f31aca625a2ebb7f05439641e1c2ce5e23ed1bf9