R=pgervais@chromium.org
BUG=503067
TEST=tested on Mac, Windows and Linux bots

Review URL: https://codereview.chromium.org/1200843003.

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295811 0039d316-1c4b-4281-b951-d872f2087c98