Check for MediaSource.isTypeSupported
Check for MediaSource.isTypeSupported

On at least one TV platform, isBrowserSupported returned true in spite
of a lack of MediaSource.isTypeSupported.  (See #804)  This adds a
check for that required method.

Change-Id: I4e68b66700508c1b3eafc9a97901f7d573ecbb80

vimond/shaka-player,russitto/shaka-player,russitto/shaka-player,vimond/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,indiereign/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,indiereign/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,indiereign/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,russitto/shaka-player