
The callback makes it easier to handle failures (in comparison to observing mount manager for MountEvents). TEST=existing BUG=tested formatting still works Review URL: https://chromiumcodereview.appspot.com/12537016 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@188161 0039d316-1c4b-4281-b951-d872f2087c98