Support for AAC SBR extension in Mpeg2 TS through the mimetype.

BUG=254214

Review URL: https://codereview.chromium.org/26680005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239245 0039d316-1c4b-4281-b951-d872f2087c98
Make sure WindowObservers are removed from window before destruction

* Check if the window observer is empty upon destruction.
* remove the all observers in ~WindowObserver()
* Remove RemoveObserver that are no longer necessary
* Fix shell shutdown order so that observers are removed correctly before deleting all windows.

BUG=324018
R=skuhne@chromium.org, sky@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=239232

Review URL: https://codereview.chromium.org/101013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239246 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239246