output object, I forgot to modify the commit command, and so now we're
ignoring failures complete. That's not good :( 

Landing w/o review (but with unit tests!) to minimize damage.
Review URL: http://codereview.chromium.org/6688017

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@78627 0039d316-1c4b-4281-b951-d872f2087c98