[Android] Add Resource loading filter for MediaPlayer

Why: There are requirements to customize the MediaPlayer resource
loading on Android which is implemented in Chromium code base.
Till now we have two points:
    1) Support the file:///android_asset in MediaPlayer.
    2) Support app scheme in the resource loading of MediaPlayer.
Unfortunately, the resource loading of MediaPlayer on Andoid goes
a different way from other ports and no interface to handle this.

How: Add a new interface ResourceLoadingFilter to filter the resource
loading(setDataSource) in MediaPlayerBridge, which could be used in
xwalk to do the customization by overriding the function of
shouldOverrideResourceLoading() in xwalk.

BUG=https://crosswalk-project.org/jira/browse/XWALK-880