[AudioPlayer] Don't start a playback automatically when reopening

BUG=chrome-os-partner:26171
TEST=manually

Review URL: https://codereview.chromium.org/181063007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254749 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254749