Added stub MediaSourcePlayer for developing behind the flag

content/browser/media/android/browser_demuxer_android.h

Index: content/browser/media/android/browser_demuxer_android.h
diff --git a/content/browser/media/android/browser_demuxer_android.h b/content/browser/media/android/browser_demuxer_android.h
index 407e0b3288663ab1c37541a92a266b6f9a270db5..6fb68e70c1ecaff9556d4f8631cd481feaea81ae 100644
--- a/content/browser/media/android/browser_demuxer_android.h
+++ b/content/browser/media/android/browser_demuxer_android.h
@@ -5,7 +5,11 @@
 #ifndef CONTENT_BROWSER_MEDIA_ANDROID_BROWSER_DEMUXER_ANDROID_H_
 #define CONTENT_BROWSER_MEDIA_ANDROID_BROWSER_DEMUXER_ANDROID_H_
 
+#define DISABLE_NON_THREAD_SAFE
 #include "base/id_map.h"
+#undef DISABLE_NON_THREAD_SAFE
+
+#include "base/synchronization/lock.h"
 #include "content/public/browser/browser_message_filter.h"
 #include "media/base/android/demuxer_android.h"
 
@@ -53,7 +57,12 @@ class CONTENT_EXPORT BrowserDemuxerAndroid : public BrowserMessageFilter {
   void OnDurationChanged(int demuxer_client_id,
                          const base::TimeDelta& duration);
 
+  media::DemuxerAndroidClient* Lookup(int demuxer_client_id);
+
+
   IDMap<media::DemuxerAndroidClient> demuxer_clients_;
+  base::Lock lock_;
+  bool enable_media_thread_for_media_playback_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserDemuxerAndroid);
 };