Support multiple STUN servers for PeerConnection.

BUG=https://code.google.com/p/webrtc/issues/detail?id=3310

Review URL: https://codereview.chromium.org/445933005

Cr-Commit-Position: refs/heads/master@{#288535}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288535 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed