[Android] Customize the resource loading of MediaPlayer

Add XWalkMediaPlayerResourceLoadingFilter which inherits
MediaPlayerBridge.ResourceLoadingFilter. Then we can customize
the MediaPlayer in xwalk. Now we have two customized items:
    Support app scheme in the resource loading of MediaPlayer.
    Support file://android_asset/ url in MediaPlayer.

BUG=https://crosswalk-project.org/jira/browse/XWALK-880