[webrtc-pc] Pull Request: proposed fix to issue #492

ShijunS has just submitted a new pull request for 
https://github.com/w3c/webrtc-pc:

== proposed fix to issue #492 ==
The proposal is to queue a task to fire the corresponding events to 
avoid risk of reentrancy (#492).

See https://github.com/w3c/webrtc-pc/pull/494