GPU: Fix latency tests

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 c5b670446e81f79ffd5bd6009d5cec68a0751a63..0c4591d1ee63fe40a6df0cbe50affce07d474c37 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -8200,6 +8200,11 @@ error::Error GLES2DecoderImpl::HandleSwapBuffers(
   }
 
   int this_frame_number = frame_number_++;
+  // TRACE_EVENT for gpu tests:
+  TRACE_EVENT_INSTANT2("test_gpu", "SwapBuffersLatency",
+                       "GLImpl", static_cast<int>(gfx::GetGLImplementation()),
+                       "width", (is_offscreen ? offscreen_size_.width() :
+                                 surface_->GetSize().width()));
   TRACE_EVENT2("gpu", "GLES2DecoderImpl::HandleSwapBuffers",
                "offscreen", is_offscreen,
                "frame", this_frame_number);