Implement TraceCallbacks in Call.

Uses a global TraceDispatcher in Call. Lazy initialization of it misses
an atomic compare and exchange to be correct. This is expected to work
fine so long as no Calls are created concurrently.

BUG=2421
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2321005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4900 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/video_engine/new_include/call.h b/video_engine/new_include/call.h
index 6650216..f8fa9be 100644
--- a/video_engine/new_include/call.h
+++ b/video_engine/new_include/call.h
@@ -42,7 +42,7 @@
           overuse_detection(false),
           voice_engine(NULL),
           trace_callback(NULL),
-          trace_filter(kTraceNone) {}
+          trace_filter(kTraceDefault) {}
 
     newapi::Transport* send_transport;
     bool overuse_detection;