Depends on rietveld cl: https://codereview.appspot.com/6726050/
BUG=155511

Review URL: https://chromiumcodereview.appspot.com/11195012

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@163092 0039d316-1c4b-4281-b951-d872f2087c98