Added GPU Tracing for DoSwapBuffers() to track frames.

gpu/command_buffer/service/gpu_tracer.h

Index: gpu/command_buffer/service/gpu_tracer.h
diff --git a/gpu/command_buffer/service/gpu_tracer.h b/gpu/command_buffer/service/gpu_tracer.h
index 64f13cc6f63eeeac1c29473b56750121fc4f96e0..fb490757bad0bba8707adcd57b339ea7055a9aed 100644
--- a/gpu/command_buffer/service/gpu_tracer.h
+++ b/gpu/command_buffer/service/gpu_tracer.h
@@ -213,6 +213,24 @@ class GPU_EXPORT GPUTrace
   DISALLOW_COPY_AND_ASSIGN(GPUTrace);
 };
 
+class ScopedGPUTrace {
+  public:
+    ScopedGPUTrace(GPUTracer* gpu_tracer, GpuTracerSource source,
+                   const std::string& category, const std::string& name)
+        : gpu_tracer_(gpu_tracer),
+          source_(source) {
+      gpu_tracer_->Begin(category, name, source_);
+    }
+
+    ~ScopedGPUTrace() {
+      gpu_tracer_->End(source_);
+    }
+
+   private:
+    GPUTracer* gpu_tracer_;
+    GpuTracerSource source_;
+};
+
 }  // namespace gles2
 }  // namespace gpu