Hookup the MediaStream glue for Adding and Removing tracks to an existing MediaStream.

content/renderer/media/mock_media_stream_dependency_factory.cc

Index: content/renderer/media/mock_media_stream_dependency_factory.cc
diff --git a/content/renderer/media/mock_media_stream_dependency_factory.cc b/content/renderer/media/mock_media_stream_dependency_factory.cc
index f2656c06e5eb8bafaa2fff485ee17339eca8e5ea..3920a71196e6454d465c63307ebbd5eb91b3258a 100644
--- a/content/renderer/media/mock_media_stream_dependency_factory.cc
+++ b/content/renderer/media/mock_media_stream_dependency_factory.cc
@@ -50,12 +50,20 @@ class MockMediaStream : public webrtc::MediaStreamInterface {
     return true;
   }
   virtual bool RemoveTrack(AudioTrackInterface* track) OVERRIDE {
-    NOTIMPLEMENTED();
-    return false;
+    AudioTrackVector::iterator it = FindTrack(&audio_track_vector_,
+                                              track->id());
+    if (it == audio_track_vector_.end())
+      return false;
+    audio_track_vector_.erase(it);
+    return true;
   }
   virtual bool RemoveTrack(VideoTrackInterface* track) OVERRIDE {
-    NOTIMPLEMENTED();
-    return false;
+    VideoTrackVector::iterator it = FindTrack(&video_track_vector_,
+                                              track->id());
+    if (it == video_track_vector_.end())
+      return false;
+    video_track_vector_.erase(it);
+    return true;
   }
   virtual std::string label() const OVERRIDE { return label_; }
   virtual AudioTrackVector GetAudioTracks() OVERRIDE {