Files.app: Surpress an error on reopeing the audio player.

BUG=None
TEST=manually

Review URL: https://codereview.chromium.org/178253005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253387 0039d316-1c4b-4281-b951-d872f2087c98
Sort the order of asynchronous procedures in VolumeManager initialization.

When VolumeManager is initialized, it obtains the current volume list first and
subscribes events for newly added volumes.  The events should be subscribed
right away, or it can cause crbug.com/330061. Besides newly added volumes
reported by the events should be added after the initial volumes are added in
order to avoid crbug.com/135477.

This CL changes the timing of subscribing the event, and adds a callback queue
to ensure the initial volumes are added before the event reported volumes.

BUG=330061
TEST=launch Files.app, mount zip archives.

Review URL: https://codereview.chromium.org/177003003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253388 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253387
SVN changes up to revision 253388