Use AlertDialog for MediaRouteControllerDialog

Rather than using custom layout for MediaRouteControllerDialog, use
AlertDialog to lay out inner views and buttons properly. Also, obtain
the media route icon from the current theme and animate it if necessary.

Bug: 33253732
Test: Launched the dialog and verified.
Change-Id: I4bec689ce808285e084fc9a90820b429e63e765a