Added stub MediaSourcePlayer for developing behind the flag

media/base/android/media_player_android.cc

Index: media/base/android/media_player_android.cc
diff --git a/media/base/android/media_player_android.cc b/media/base/android/media_player_android.cc
index 9f224c9b675cb08e80f6cf87460cddbff65e440d..60e1dfc0f823268042381b5e4514931290c3d2b8 100644
--- a/media/base/android/media_player_android.cc
+++ b/media/base/android/media_player_android.cc
@@ -30,6 +30,11 @@ MediaPlayerAndroid::MediaPlayerAndroid(
 
 MediaPlayerAndroid::~MediaPlayerAndroid() {}
 
+// For most subclasses we can delete on the caller thread.
+void MediaPlayerAndroid::DeleteOnCorrectThread() {
+  delete this;
+}
+
 GURL MediaPlayerAndroid::GetUrl() {
   return GURL();
 }
@@ -81,6 +86,11 @@ void MediaPlayerAndroid::DetachListener() {
   listener_->ReleaseMediaPlayerListenerResources();
 }
 
+void MediaPlayerAndroid::DestroyListenerOnUIThread() {
+  weak_factory_.InvalidateWeakPtrs();
+  listener_.reset();
+}
+
 void MediaPlayerAndroid::SetAudible(bool is_audible) {
   if (is_audible_ != is_audible) {
     is_audible_ = is_audible;