A git patch repo is cloned to .git/git-try/patches-git, if was not
cloned before. Otherwise, changes are pulled. Then a patch is committed and
pushed.

--revision=auto (Git only) is resolved to the revision the diff is generated
against.

R=stip@chromium.org, agable@chromium.org, iannucci@chromium.org, maruel@chromium.org
BUG=325882

Review URL: https://codereview.chromium.org/184343003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@260471 0039d316-1c4b-4281-b951-d872f2087c98