The key piece here is that when running 'git cl land' from a cache checkout, refs/pending/* must be fetched from / pushed to the cache mirror's remote.

BUG=589140
R=wkorman,agable,iannucci,martiniss

Review URL: https://codereview.chromium.org/1777693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299166 0039d316-1c4b-4281-b951-d872f2087c98