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..0d778f3570ed2ab036adb03d327847c825248b4c 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -9753,6 +9753,9 @@ void GLES2DecoderImpl::DoSwapBuffers() {
     TRACE_EVENT_SYNTHETIC_DELAY("gpu.PresentingFrame");
   }
 
+  ScopedGPUTrace scoped_gpu_trace(gpu_tracer_.get(), kTraceDecoder,
+                                  "gpu_toplevel", "SwapBuffer");
+
   bool is_tracing;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT("gpu.debug"),
                                      &is_tracing);