implement connectionstatechange algorithm from https://github.com/w3c/webrtc-pc/pull/291
implement connectionstatechange algorithm from https://github.com/w3c/webrtc-pc/pull/291

xdumaine/adapter,Acidburn0zzz/adapter,jan-ivar/adapter,Acidburn0zzz/adapter,webrtc/adapter,Acidburn0zzz/adapter,xdumaine/adapter,webrtc/adapter,jan-ivar/adapter