feat(MediaCap): Always polyfill MediaCap for Chromecast
feat(MediaCap): Always polyfill MediaCap for Chromecast

Since we got some unexpected decodingInfo results from MediaCapabilities
on Chromecast, we should fall back to MediaSource.isTypeSupported() on
Chromecast.

Issue #1391

Change-Id: I4947ec78624e98c7039df64ad691e14ece2588e0

tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player