message: Add a printout at the start of MetaOptimizer::Optimize() to  make it easier to see the total cost of running Grappler in logs. Also add a couple of VLOG(1) statements to see breakdown between main graph and function optimization.
diff: @@ -331,10 +331,12 @@ Status MetaOptimizer::RunOptimizer(
  Status MetaOptimizer::Optimize(Cluster* cluster, const GrapplerItem& item,
  GraphDef* optimized_graph) {
  + LOG(INFO) << "Starting optimization for grappler item: " << item.id;
  optimization_results_.clear();
  // 1. Optimize main graph
  TF_RETURN_IF_ERROR(OptimizeGraph(cluster, item, optimized_graph));
  + VLOG(1) << "Optimized main graph.";
  // 2. Optimize function library
  FunctionLibraryDefinition flib(OpRegistry::Global(),
  @@ -398,7 +400,7 @@ Status MetaOptimizer::Optimize(Cluster* cluster, const GrapplerItem& item,
  }
  }
  - VLOG(3) << "Optimized " << optimized_funcs.size()
  + VLOG(1) << "Optimized " << optimized_funcs.size()
  << " functions: " << str_util::Join(optimized_funcs, ", ");
  return Status::OK();
  