This CL changes the return code of these methods to indicate success instead of failure when there is nothing to change. This change appears to resolve an issue where enabling the timestamp offset extension via SDP would result in a failure if that extension had already been enabled. Review URL: https://webrtc-codereview.appspot.com/1118008 git-svn-id: http://webrtc.googlecode.com/svn/trunk@3588 4adac7df-926f-26a2-2b94-8c16560cd09d