With this CL, the patch that is sent to the code review site includes only changes from the nearest common ancestor of the local and the upstream branch.

A diagram:

     /----B <- local branch
----A-----C <- upstream

Previously, the diff would be simply between C and B, whereas now it's between A and C, even if you update C.

This allows you to continously update origin/trunk without having to rebase/merge your local changes all the time, resulting in the need for less rebuilds.

Review URL: http://codereview.chromium.org/1583003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@43113 0039d316-1c4b-4281-b951-d872f2087c98