Add new view that renders local video using AVCaptureLayerPreview.

talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm

Index: talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm
diff --git a/talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm b/talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm
index 525cead7da2a1368b7ec91f3ecdd234c3452a807..554fdaa3e676107568f961072b7746bf86062d3a 100644
--- a/talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm
+++ b/talk/app/webrtc/objc/RTCAVFoundationVideoSource.mm
@@ -57,6 +57,10 @@
   return self.capturer->GetCaptureSession();
 }
 
+- (dispatch_queue_t)captureSessionQueue {
+  return self.capturer->GetCaptureSessionQueue();
+}
+
 - (webrtc::AVFoundationVideoCapturer*)capturer {
   cricket::VideoCapturer* capturer = self.videoSource->GetVideoCapturer();
   // This should be safe because no one should have changed the underlying video