[Mac] Remove the yellow ball and replace it with a green arrow thing.

BUG=65742
TEST=Wait to be out-of-date (or uncomment some code in upgrade_detector.cc) and run with --check-for-update-interval=5. See green icon on Wrench menu button that matches the one in the menu.

Review URL: http://codereview.chromium.org/6048001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@69648 0039d316-1c4b-4281-b951-d872f2087c98