Made demo controls count as opaque while casting.
Made demo controls count as opaque while casting.

The demo controls are always opaque while casting, because of the css.
The .isOpaque_() method on controls did not account for that, however, which
caused a problem where the seek bar would not update unless the user hovers
over the controls.
This fixes that problem.

Change-Id: I953a797fd68abcde4a7e8ac985ed80a2d8cdc98e

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