title: onicegatheringstatechange event does not trigger during candidates gathering
body: <p>I am writing a webrtc application where I can not use trickle ice. So I am waiting for ICE candidates gathering to complete and send the offer to other peer so that ICE candidates are included in SDP. I have set an event handle for onicegatheringstatechange and waiting for iceGatheringState to change. But this event is not triggered.</p>
  
  <pre><code>pc = new RTCPeerConnection(peerConnectionConfig, peerConnectionConstraints);
  pc.onicegatheringstatechange = onIceGatheringStateChange;
  </code></pre>
  
  <p>Is there something else I have to do in order to make it work ?</p>