message: Make error messages less noisy.
diff: @@ -238,7 +238,7 @@ class GraphOptimizerStagePipeline {
  // Each stage must be "error safe" (just like exception safe). In
  // case of any error it must leave optimized graph unmodified.
  if (!stage_status.ok()) {
  - LOG(WARNING) << "Failed to run optimizer " << stage->optimizer_name()
  + VLOG(2) << "Failed to run optimizer " << stage->optimizer_name()
  << ", stage " << stage->stage_name() << " node "
  << node->name()
  << ". Error: " << stage_status.error_message();
  