Should fix deadlock on build bots. Before, TraceImpl called TraceDispatcher::Print, while TraceDispatcher::Deregister called TraceImpl through VideoEngine::SetTraceCallback. This violates locking order as both take their own locks. BUG=2421 R=stefan@webrtc.org Review URL: https://webrtc-codereview.appspot.com/2340005 git-svn-id: http://webrtc.googlecode.com/svn/trunk@4905 4adac7df-926f-26a2-2b94-8c16560cd09d