Chromite will be added to the Chrome checkout at third_party/chromite -
detect when the checkout is a gclient checkout, and look for chromite at
that path.

BUG=None
TEST=ran 'cbuildbot' in both a repo and gclient checkout.


Review URL: https://chromiumcodereview.appspot.com/12094111

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@181563 0039d316-1c4b-4281-b951-d872f2087c98