Shutdown the notification UI manager before the notifications service, as the former's shutdown logic depends on the latter.

      BUG=50553
TEST=see bug

Review URL: http://codereview.chromium.org/3051029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@54713 0039d316-1c4b-4281-b951-d872f2087c98