Port Chromium's trace_event.h to WebKit and add 

trace_event.h is ported from Chromium code.

These files are defined new for WebRTC:
* event_tracer.h
* event_tracer.cc
* event_tracer_unittest.cc
Review URL: https://webrtc-codereview.appspot.com/933034

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3262 4adac7df-926f-26a2-2b94-8c16560cd09d
6 files changed