Motivation: git_cl should start understanding Gerrit's git footers,
to avoid appending BUG= after Change-Id: Ixxx line.

R=sergiyb@chromium.org
BUG=614587

Review-Url: https://codereview.chromium.org/2028303006

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300691 0039d316-1c4b-4281-b951-d872f2087c98