Support multiple URLs in PeerConnectionInterface::IceServer

This adds support for multiple URLs in a IceServer configuration as
defined in http://w3c.github.io/webrtc-pc/#idl-def-RTCIceServer.

BUG=2096
R=pthatcher@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/57489004

Cr-Commit-Position: refs/heads/master@{#9320}
3 files changed