message: Add a TFE_Py_Execute traceme, which is the entrance to TF c++
diff: @@ -852,6 +852,8 @@ void TFE_Py_ExecuteCancelable(TFE_Context* ctx, const char* device_name,
  TFE_CancellationManager* cancellation_manager,
  TFE_OutputTensorHandles* outputs,
  TF_Status* out_status) {
  + tensorflow::profiler::TraceMe activity(
  + "TFE_Py_ExecuteCancelable", tensorflow::profiler::TraceMeLevel::kInfo);
  TFE_Op* op = GetOp(ctx, op_name, device_name, out_status);
  auto cleaner = tensorflow::gtl::MakeCleanup([ctx, op] { ReturnOp(ctx, op); });
  if (!out_status->status.ok()) return;
  