Add trace events to measure GPU process startup timing and time to first present.

content/gpu/gpu_info_collector_mac.mm

Index: content/gpu/gpu_info_collector_mac.mm
===================================================================
--- content/gpu/gpu_info_collector_mac.mm	(revision 137679)
+++ content/gpu/gpu_info_collector_mac.mm	(working copy)
@@ -6,6 +6,7 @@
 
 #include <vector>
 
+#include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/memory/scoped_ptr.h"
@@ -157,6 +158,8 @@
 bool CollectGraphicsInfo(content::GPUInfo* gpu_info) {
   DCHECK(gpu_info);
 
+  TRACE_EVENT0("gpu", "gpu_info_collector::CollectGraphicsInfo");
+
   gpu_info->can_lose_context =
       (gfx::GetGLImplementation() == gfx::kGLImplementationEGLGLES2);
   gpu_info->finalized = true;