Redo the change of https://webrtc-codereview.appspot.com/30949004/

The previous change causes a build issue as there is subclass of TransportChannel in chromium. To break the circular dependency, a stub of implementation for GetState() is provided and will be removed once the jingle_glue::MockTransportChannel has the function defined.

TBR=pthatcher@webrtc.org

BUG=411086

Review URL: https://webrtc-codereview.appspot.com/34369004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7806 4adac7df-926f-26a2-2b94-8c16560cd09d