With the addition of this method, rietveld.py can be used to create cli-based tools to review Chromium code.

BUG=none

Review URL: https://codereview.chromium.org/127083003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@244529 0039d316-1c4b-4281-b951-d872f2087c98