[webrtc-pc] new commits pushed by aboba

The following commits were just pushed by aboba to https://github.com/w3c/webrtc-pc:

* RTCIceConnectionEventInit: url is nullable

describes the url as nullable as it is done in the idl definition.
Also adds a explanatory text.
  by Philipp Hancke
https://github.com/w3c/webrtc-pc/commit/39d6a25ed0c04c584aa69361ea3a87f3d07ada7f

* Merge pull request #1239 from fippo/idlnit

RTCIceConnectionEventInit: url is nullable
  by Bernard Aboba
https://github.com/w3c/webrtc-pc/commit/efb47c050fe2850b5e389805bfe10fbb6845a141