Wait for volume manager initialization before resolving urls in the audio player.

Converting from URLs to Entries required permissions, which are granted asynchronously by the volume manager. Therefore, we have to call ensureInitialized() before trying to resolve them.

TEST=Tested manually.
BUG=336301

Review URL: https://codereview.chromium.org/143463003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245987 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245987