This should make a `gclient sync` faster, especially on Windows, where git hangs regularly.

BUG=none
TEST=gclient sync -v doesn't print "Fetching origin" all the time


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=143898
Reverted: http://src.chromium.org/viewvc/chrome?view=rev&revision=143911

Review URL: https://chromiumcodereview.appspot.com/10668020

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@144451 0039d316-1c4b-4281-b951-d872f2087c98