Added mute logic to VideoTrackRenderers.

talk/app/webrtc/videotrackrenderers.cc

Index: talk/app/webrtc/videotrackrenderers.cc
diff --git a/talk/app/webrtc/videotrackrenderers.cc b/talk/app/webrtc/videotrackrenderers.cc
index 3f9301b7185d88789877c39f985ae150e4e8158f..5987e9190d60d1757c59ffc5b51e43664db8b4a7 100644
--- a/talk/app/webrtc/videotrackrenderers.cc
+++ b/talk/app/webrtc/videotrackrenderers.cc
@@ -26,7 +26,7 @@
  */
 
 #include "talk/app/webrtc/videotrackrenderers.h"
-#include "talk/media/base/videoframe.h"
+#include "talk/media/webrtc/webrtcvideoframe.h"
 
 namespace webrtc {
 
@@ -54,11 +54,21 @@ void VideoTrackRenderers::SetEnabled(bool enable) {
   enabled_ = enable;
 }
 
+// Create a black frame, with the same size, timestamp and rotation.
+static cricket::VideoFrame* CreateBlackFrame(const cricket::VideoFrame* frame) {

[perkj_webrtc, 2016/01/13 09:44:40]

static methods should be at the top of the file. And prefer anonymouse ns to
static.

+  cricket::VideoFrame* black = new cricket::WebRtcVideoFrame(

[perkj_webrtc, 2016/01/13 09:44:40]

This looks like a memory leak. Ownership is not transfered to the renderers. 
You will have to have this black frame as a member I think.

[nisse-webrtc, 2016/01/13 10:33:16]

The VideoFrameBuffer is reference counted, but I have to delete the
cricket::VideoFrame? When is that safe? As soon as the downstream RenderFrame
calls return? Then I can just allocate the object on the stack instead.

I was also thinking about caching the VideoFrameBuffer and keep using it as long
as the size is unchanged. But that might be a premature optimzation.

+      new rtc::RefCountedObject<I420Buffer>(frame->GetWidth(),
+                                            frame->GetHeight()),
+      frame->GetTimeStamp(), frame->GetVideoRotation());
+  black->SetToBlack();
+  return black;
+}
+
 bool VideoTrackRenderers::RenderFrame(const cricket::VideoFrame* frame) {
   rtc::CritScope cs(&critical_section_);
-  if (!enabled_) {
-    return true;
-  }
+  if (!enabled_)
+    frame = CreateBlackFrame(frame);
+
   for (VideoRendererInterface* renderer : renderers_) {
     renderer->RenderFrame(frame);
   }