[AudioPlayer] Fix a bug on changing 'expanded' status

The playlist goes wrong when the 'expanded' status is changed in some condition.

BUG=342610, chrome-os-partner:26202
TEST=manually tested

Review URL: https://codereview.chromium.org/185653014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255394 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255394