Allow WebRtcMediaEngine to be created from any thread.

webrtc/media/base/fakemediaengine.h

Index: webrtc/media/base/fakemediaengine.h
diff --git a/webrtc/media/base/fakemediaengine.h b/webrtc/media/base/fakemediaengine.h
index 4984d1b88c3168dbcaff6ef43501ab5b07292b58..12cd4cb1c97a87e41189f13a57c68c7a64cf0762 100644
--- a/webrtc/media/base/fakemediaengine.h
+++ b/webrtc/media/base/fakemediaengine.h
@@ -775,6 +775,7 @@ class FakeVoiceEngine : public FakeBaseEngine {
     // sanity checks against that.
     codecs_.push_back(AudioCodec(101, "fake_audio_codec", 0, 0, 1));
   }
+  void Init() {}
   rtc::scoped_refptr<webrtc::AudioState> GetAudioState() const {
     return rtc::scoped_refptr<webrtc::AudioState>();
   }