With the deletion of .DEPS.git, 'webkit_rev' became 'webkit_revision':
https://codereview.chromium.org/497313003

Without this change, gclient sync will not get the latest Blink commit.

Review URL: https://codereview.chromium.org/496443005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@291716 0039d316-1c4b-4281-b951-d872f2087c98