Fix autoplay during prerendering for media elements on Android.
If the user gesture for autoplay is disabled manually or via an
experiment, prerendered media will play in a hidden frame.
Within WebMediaPlayerImpl this behavior is deferred at load time
via a callback, however WebMediaPlayerAndroid was never given
this callback, so it would try to play media. Generally this
fails because by default autoplay requires a user gesture.
The correct fix is to refactor WMPA such that it uses a params
structure like WMPI and can invoke the deferral callback when
load() is called.
TEST=clank no longer plays hidden a/v when user gesture disabled.