Improve iOS frame capture threading.

talk/app/webrtc/objc/avfoundationvideocapturer.h

Index: talk/app/webrtc/objc/avfoundationvideocapturer.h
diff --git a/talk/app/webrtc/objc/avfoundationvideocapturer.h b/talk/app/webrtc/objc/avfoundationvideocapturer.h
index 69ade5f1e01221ebc9fda19c74b5d9e850d47b2e..8bc128dd42d76ad984f49d796083b41bad59bf16 100644
--- a/talk/app/webrtc/objc/avfoundationvideocapturer.h
+++ b/talk/app/webrtc/objc/avfoundationvideocapturer.h
@@ -41,7 +41,8 @@ class Thread;
 
 namespace webrtc {
 
-class AVFoundationVideoCapturer : public cricket::VideoCapturer {
+class AVFoundationVideoCapturer : public cricket::VideoCapturer,
+                                  public rtc::MessageHandler {
  public:
   AVFoundationVideoCapturer();
   ~AVFoundationVideoCapturer();
@@ -57,7 +58,8 @@ class AVFoundationVideoCapturer : public cricket::VideoCapturer {
     return true;
   }
 
-  // Returns the active capture session.
+  // Returns the active capture session. Calls to the capture session should
+  // occur on the RTCDispatcherTypeCaptureSession queue in RTCDispatcher.
   AVCaptureSession* GetCaptureSession();
 
   // Returns whether the rear-facing camera can be used.
@@ -72,9 +74,11 @@ class AVFoundationVideoCapturer : public cricket::VideoCapturer {
   // frame for capture.
   void CaptureSampleBuffer(CMSampleBufferRef sampleBuffer);
 
+  // Handles messages from posts.
+  void OnMessage(rtc::Message *msg) override;
+
  private:
-  // Used to signal frame capture on the thread that capturer was started on.
-  void SignalFrameCapturedOnStartThread(const cricket::CapturedFrame* frame);
+  void OnFrameMessage(CVImageBufferRef image_buffer, int64_t capture_time);
 
   RTCAVFoundationVideoCapturerInternal* _capturer;
   rtc::Thread* _startThread;  // Set in Start(), unset in Stop().