This command shows the differences between local branch
and the last patch uploaded to rietveld. The idea being
that you can see what would be uploaded before you actually
upload.

This can useful when using 'git cl patch' to move changes
between checkouts and working from more than one machine at
once.

Review URL: https://chromiumcodereview.appspot.com/24276008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@225552 0039d316-1c4b-4281-b951-d872f2087c98