Always initialize Trace in Call TraceDispatcher.

Prevents violation of lock order occuring previously when
RegisterCallback called SetTraceCallback while holding its lock, which
called Print back (which acquires the lock).

BUG=
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/7559004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5433 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed