Make setRemoteDescription, setLocalDescription et al async.

content/renderer/media/rtc_peer_connection_handler.h

Index: content/renderer/media/rtc_peer_connection_handler.h
diff --git a/content/renderer/media/rtc_peer_connection_handler.h b/content/renderer/media/rtc_peer_connection_handler.h
index 14a6256e1d9268e0f392bacdfad6de8ec1f916f0..52842e229a5e1354fe027ba03f93d22b8b04be77 100644
--- a/content/renderer/media/rtc_peer_connection_handler.h
+++ b/content/renderer/media/rtc_peer_connection_handler.h
@@ -91,8 +91,7 @@ class CONTENT_EXPORT RTCPeerConnectionHandler
  public:
   RTCPeerConnectionHandler(
       blink::WebRTCPeerConnectionHandlerClient* client,
-      PeerConnectionDependencyFactory* dependency_factory,
-      const scoped_refptr<base::SingleThreadTaskRunner>& signaling_thread);
+      PeerConnectionDependencyFactory* dependency_factory);
   virtual ~RTCPeerConnectionHandler();
 
   // Destroy all existing RTCPeerConnectionHandler objects.
@@ -204,6 +203,12 @@ class CONTENT_EXPORT RTCPeerConnectionHandler
       const std::string& sdp, const std::string& type,
       webrtc::SdpParseError* error);
 
+  // Virtual to allow mocks to override.
+  virtual scoped_refptr<base::SingleThreadTaskRunner> signaling_thread() const;
+
+  void RunSynchronousClosureOnSignalingThread(const base::Closure& closure,
+                                              const char* trace_event_name);
+
   base::ThreadChecker thread_checker_;
 
   // |client_| is a weak pointer, and is valid until stop() has returned.
@@ -215,9 +220,6 @@ class CONTENT_EXPORT RTCPeerConnectionHandler
 
   blink::WebFrame* frame_;
 
-  // Libjingle's signaling thread.
-  const scoped_refptr<base::SingleThreadTaskRunner> signaling_thread_;
-
   ScopedVector<WebRtcMediaStreamAdapter> local_streams_;
 
   base::WeakPtr<PeerConnectionTracker> peer_connection_tracker_;