add TRACE_EVENT to ANGLE (reland)

Tracing code the same as previous CL:
https://codereview.appspot.com/12699047/

Setup code simplified, and follows the GetProcAddress model of other
gl functions.

R=shannonwoods@google.com
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 4cd41af..fcb6315 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -39,6 +39,7 @@
  Adrienne Walker
  thestig@chromium.org
  Justin Schuh
+ Scott Graham
 
 Adobe Systems Inc.
  Alexandru Chiculita