Enable Skia tracing in browser process

skia/ext/event_tracer_impl.cc

Index: skia/ext/event_tracer_impl.cc
diff --git a/skia/ext/event_tracer_impl.cc b/skia/ext/event_tracer_impl.cc
index f6e12f05d605a198d7777bbcda02162b17d220db..c4d89a4f8f630286042bd170cdd78692f2a8586b 100644
--- a/skia/ext/event_tracer_impl.cc
+++ b/skia/ext/event_tracer_impl.cc
@@ -70,5 +70,6 @@ void
 void InitSkiaEventTracer() {
   // Initialize the binding to Skia's tracing events. Skia will
   // take ownership of and clean up the memory allocated here.
-  SkEventTracer::SetInstance(new skia::SkChromiumEventTracer());
+  if (!SkEventTracer::GetInstance())
+    SkEventTracer::SetInstance(new skia::SkChromiumEventTracer());
 }