Implement timing frames.

webrtc/media/engine/webrtcvideoengine.cc

Index: webrtc/media/engine/webrtcvideoengine.cc
diff --git a/webrtc/media/engine/webrtcvideoengine.cc b/webrtc/media/engine/webrtcvideoengine.cc
index 999dac228a4bfa4b3986058bdd0b18b92abf6cfd..2bb057454df642e03e120731455bf73a6905ea8e 100644
--- a/webrtc/media/engine/webrtcvideoengine.cc
+++ b/webrtc/media/engine/webrtcvideoengine.cc
@@ -523,6 +523,8 @@ RtpCapabilities WebRtcVideoEngine::GetCapabilities() const {
         webrtc::RtpExtension(webrtc::RtpExtension::kVideoContentTypeUri,
                              webrtc::RtpExtension::kVideoContentTypeDefaultId));
   }
+  // TODO(ilnik): Add kVideoTimingUri/kVideoTimingDefaultId to capabilities.
+  // Possibly inside field trial.
   return capabilities;
 }