depot_tools: Run roll_dep tests on Python 3.

Bug: 1009816
Change-Id: I2fac9f03b6dd275563375d8ac4d1e71b5188e468
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1925325
Reviewed-by: Anthony Polito <apolito@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

roll_dep.py

@@ -52,7 +52,7 @@ class AlreadyRolledError(Error):
 def check_output(*args, **kwargs):
   """subprocess.check_output() passing shell=True on Windows for git."""
   kwargs.setdefault('shell', NEED_SHELL)
-  return subprocess.check_output(*args, **kwargs)
+  return subprocess.check_output(*args, **kwargs).decode('utf-8')
 
 
 def check_call(*args, **kwargs):

tests/roll_dep_test.py

@@ -56,6 +56,10 @@ class RollDepTest(fake_repos.FakeReposTestBase):
     self.env = os.environ.copy()
     self.env['DEPOT_TOOLS_UPDATE'] = '0'
     self.env['DEPOT_TOOLS_METRICS'] = '0'
+    # Suppress Python 3 warnings and other test undesirables.
+    self.env['GCLIENT_TEST'] = '1'
+
+    self.maxDiff = None
 
     self.enabled = self.FAKE_REPOS.set_up_git()
     self.src_dir = os.path.join(self.root_dir, 'src')
@@ -73,6 +77,8 @@ class RollDepTest(fake_repos.FakeReposTestBase):
     stdout, stderr = process.communicate()
     logging.debug("XXX: %s\n%s\nXXX" % (' '.join(cmd), stdout))
     logging.debug("YYY: %s\n%s\nYYY" % (' '.join(cmd), stderr))
+    stdout = stdout.decode('utf-8')
+    stderr = stderr.decode('utf-8')
     return (stdout.replace('\r\n', '\n'), stderr.replace('\r\n', '\n'),
             process.returncode)