Remove show/hide API

This CL removes the show/hide API from MediaControlView2 and instead
provides the developer with the same function by calling
setVisibility(View.VISIBLE | View.GONE), and calling the new APIs
set/getTimeout() and requestPlayButtonFocus(). The original Runnable
code has been moved to onVisibilityAggregated() as per API council's
request.

Test: build
Change-Id: Ice2ae746e2d3e80e356ce117d98898c63b783d07