GitilesPoller: preserve git commit as a property on change object.
GitilesPoller: preserve git commit as a property on change object.

When svn_mode is enabled, this ensures that the git revision is
preserved.  Ostensibly, this blocks:

https://code.google.com/p/chromium/issues/detail?id=337035

... although I'm sure how.  lkgr_finder.py relies on the buildbot
json feed, and that feed does not encode source stamp properties.
Maybe that's the next necessary change...

R=agable@chromium.org,zty@chromium.org
BUG=337035

Review URL: https://codereview.chromium.org/442343005

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@289377 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build