Implement FrameMarking header extension support

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 e592740bb9260b3c6594514930a1793dca4c96af..e368c1d78a758dda466c5357ffcdef0d1ef69982 100644
--- a/webrtc/media/engine/webrtcvideoengine.cc
+++ b/webrtc/media/engine/webrtcvideoengine.cc
@@ -458,6 +458,9 @@ RtpCapabilities WebRtcVideoEngine::GetCapabilities() const {
         webrtc::RtpExtension(webrtc::RtpExtension::kVideoContentTypeUri,
                              webrtc::RtpExtension::kVideoContentTypeDefaultId));
   }
+  capabilities.header_extensions.push_back(
+      webrtc::RtpExtension(webrtc::RtpExtension::kFrameMarkingUri,
+                           webrtc::RtpExtension::kFrameMarkingDefaultId));
   // TODO(ilnik): Add kVideoTimingUri/kVideoTimingDefaultId to capabilities.
   // Possibly inside field trial.
   return capabilities;