Late initialize MediaController, for less resource i.e. ProcessThread, usage by PeerConnection.

webrtc/api/peerconnection.h

Index: webrtc/api/peerconnection.h
diff --git a/webrtc/api/peerconnection.h b/webrtc/api/peerconnection.h
index 7ad1940f77a89b68a5bdd57a27a405b13188281a..f5f41bb1f5d1f938472f56a18c507490ff4797bd 100644
--- a/webrtc/api/peerconnection.h
+++ b/webrtc/api/peerconnection.h
@@ -196,6 +196,8 @@ class PeerConnection : public PeerConnectionInterface,
       CreateSessionDescriptionObserver* observer,
       const std::string& error);
 
+  void LateInitialize();
+
   bool IsClosed() const {
     return signaling_state_ == PeerConnectionInterface::kClosed;
   }
@@ -375,6 +377,7 @@ class PeerConnection : public PeerConnectionInterface,
   rtc::scoped_ptr<WebRtcSession> session_;
   // ... But stats_ depends on session_ so it should be destroyed even earlier.
   rtc::scoped_ptr<StatsCollector> stats_;
+  cricket::MediaConfig media_config_;
 };
 
 }  // namespace webrtc