MediaRecorder: make MediaRecorderHandler a MediaStreamObserver

content/renderer/media/media_recorder_handler.h

Index: content/renderer/media/media_recorder_handler.h
diff --git a/content/renderer/media/media_recorder_handler.h b/content/renderer/media/media_recorder_handler.h
index 453923b9638f67c860d1ec2c27617a226abe94dd..ebeac115d4cdc4c937c0bdbce338a44787fb9838 100644
--- a/content/renderer/media/media_recorder_handler.h
+++ b/content/renderer/media/media_recorder_handler.h
@@ -11,6 +11,7 @@
 #include "base/strings/string_piece.h"
 #include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
+#include "content/renderer/media/media_stream.h"
 #include "third_party/WebKit/public/platform/WebMediaRecorderHandler.h"
 #include "third_party/WebKit/public/platform/WebMediaStream.h"
 
@@ -41,7 +42,8 @@ class AudioTrackRecorder;
 // i.e. the Main Render thread. (Note that a BindToCurrentLoop is used to
 // guarantee this, since VideoTrackRecorder sends back frames on IO thread.)
 class CONTENT_EXPORT MediaRecorderHandler final
-    : public NON_EXPORTED_BASE(blink::WebMediaRecorderHandler) {
+    : public NON_EXPORTED_BASE(blink::WebMediaRecorderHandler),
+      public NON_EXPORTED_BASE(MediaStreamObserver) {
  public:
   MediaRecorderHandler();
   ~MediaRecorderHandler() override;
@@ -59,6 +61,11 @@ class CONTENT_EXPORT MediaRecorderHandler final
   void pause() override;
   void resume() override;
 
+  // MediaStreamObserver implementation. On MS modification, we stop recording
+  // and signal this illegal condition to |client_|.
+  void TrackAdded(const blink::WebMediaStreamTrack& track) override;
+  void TrackRemoved(const blink::WebMediaStreamTrack& track) override;
+
  private:
   friend class MediaRecorderHandlerTest;