[Chromedriver] Convert Git hash to svn revision if required.

NOTRY=True

Review URL: https://codereview.chromium.org/337923007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278870 0039d316-1c4b-4281-b951-d872f2087c98
[ChromeDriver] Fix error of step wait_for_snapshot.

BUG=
NOTRY=True
TBR=samuong

Review URL: https://codereview.chromium.org/346053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278893 0039d316-1c4b-4281-b951-d872f2087c98