Added GPU Tracing for DoSwapBuffers() to track frames.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index b0377a8fd0342b0026d268f1251ba1d403a201dd..56a0170752e9714fe15948b752c497a3507c81b2 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -9753,6 +9753,21 @@ void GLES2DecoderImpl::DoSwapBuffers() {
     TRACE_EVENT_SYNTHETIC_DELAY("gpu.PresentingFrame");
   }
 
+  struct GPUSwapBufferTrace {
+   public:
+    GPUSwapBufferTrace(GPUTracer* gpu_tracer, int frame)

[vmiura, 2015/01/16 20:39:34]

As discussed offline, maybe make this a generic ScopedGPUTrace class, and remove
'frame' if unused?

[David Yen, 2015/01/16 21:34:19]

Done.

+        : gpu_tracer_(gpu_tracer) {
+      gpu_tracer_->Begin("SwapBuffer", "DoSwapBuffers", kTraceSwapBuffer);
+    }
+
+    ~GPUSwapBufferTrace() {
+      gpu_tracer_->End(kTraceSwapBuffer);
+    }
+
+   private:
+    GPUTracer* gpu_tracer_;
+  } swap_buffer_trace(gpu_tracer_.get(), this_frame_number);
+
   bool is_tracing;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("gpu.debug"),
                                      &is_tracing);