Split libjingle's signaling thread from the UI thread

content/renderer/media/webrtc_local_audio_track.cc

Index: content/renderer/media/webrtc_local_audio_track.cc
diff --git a/content/renderer/media/webrtc_local_audio_track.cc b/content/renderer/media/webrtc_local_audio_track.cc
index 99ada98099fa3163d58fbf46ed0185fe838b8f39..cd610550b51927bab88b8a634656c6953a440821 100644
--- a/content/renderer/media/webrtc_local_audio_track.cc
+++ b/content/renderer/media/webrtc_local_audio_track.cc
@@ -25,6 +25,7 @@ WebRtcLocalAudioTrack::WebRtcLocalAudioTrack(
       capturer_(capturer),
       webaudio_source_(webaudio_source) {
   DCHECK(capturer.get() || webaudio_source);
+  signal_thread_checker_.DetachFromThread();
 
   adapter_->Initialize(this);
 
@@ -122,7 +123,11 @@ void WebRtcLocalAudioTrack::SetAudioProcessor(
 }
 
 void WebRtcLocalAudioTrack::AddSink(MediaStreamAudioSink* sink) {
-  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  // This method is called from webrtc, on the signaling thread, when the local
+  // description is set and from the main thread from WebMediaPlayerMS::load
+  // (via WebRtcLocalAudioRenderer::Start).
+  DCHECK(main_render_thread_checker_.CalledOnValidThread() ||
+         signal_thread_checker_.CalledOnValidThread());
   DVLOG(1) << "WebRtcLocalAudioTrack::AddSink()";
   base::AutoLock auto_lock(lock_);