Add SignalUpdateSessionDescription to PeerConnectionSignaling.
This is to allow webrtcsession to setup the mediachannels based on tracks.

BUG=
TEST=

Review URL: http://webrtc-codereview.appspot.com/184001

git-svn-id: http://webrtc.googlecode.com/svn/trunk@665 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed