[Android] Support third part media player on Crosswalk

A requirement from an important customer who want to forward web resources with proxy
on Crosswalk, but android system MediaPlayer can't set a proxy with a standard API.
The ExoMediaPlayer is playing videos and music is a popular activity on Android devices,
and it can be configured with proxy.
https://developer.android.com/guide/topics/media/exoplayer.html

BUG=XWALK-6770

runtime/android/core_internal/src/org/xwalk/core/internal/XWalkContent.java

@@ -144,7 +144,7 @@ public XWalkContent(Context context, String animatable, XWalkViewInternal xwView
         mGeolocationPermissions = new XWalkGeolocationPermissions(sharedPreferences);
 
         MediaPlayerBridge.setResourceLoadingFilter(
-                new XWalkMediaPlayerResourceLoadingFilter());
+                new XWalkMediaPlayerResourceLoadingFilter(mContentsClientBridge));
 
         setNativeContent(nativeInit(), animatable);
 
@@ -391,6 +391,11 @@ public void setXWalkWebChromeClient(XWalkWebChromeClient client) {
         mContentsClientBridge.setXWalkWebChromeClient(client);
     }
 
+    public void setXWalkMediaPlayer(XWalkMediaPlayerInternal mediaPlayer) {
+        if (mNativeContent == 0) return;
+        mContentsClientBridge.setXWalkMediaPlayer(mediaPlayer);
+    }
+
     public XWalkWebChromeClient getXWalkWebChromeClient() {
         if (mNativeContent == 0) return null;
         return mContentsClientBridge.getXWalkWebChromeClient();

runtime/android/core_internal/src/org/xwalk/core/internal/XWalkContentsClientBridge.java

@@ -70,6 +70,7 @@ class XWalkContentsClientBridge extends XWalkContentsClient
     private XWalkNavigationHandler mNavigationHandler;
     private XWalkNotificationService mNotificationService;
     private Handler mUiThreadHandler;
+    private XWalkMediaPlayerInternal mXWalkMediaPlayerInternal;
 
     /** State recording variables */
     // For fullscreen state.
@@ -163,6 +164,13 @@ public void setResourceClient(XWalkResourceClientInternal client) {
         mXWalkResourceClient = new XWalkResourceClientInternal(mXWalkView);
     }
 
+    public void setXWalkMediaPlayer(XWalkMediaPlayerInternal mediaPlayer) {
+        mXWalkMediaPlayerInternal = mediaPlayer;
+    }
+
+    public XWalkMediaPlayerInternal getExternalMediaPlayer() {
+        return mXWalkMediaPlayerInternal;
+    }
 
     public void setXWalkWebChromeClient(XWalkWebChromeClient client) {
         // If it's null, use Crosswalk implementation.