For c++, Generate enum classes instead of enum from mojom.

mojo/services/view_manager/public/cpp/lib/view_manager_client_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "view_manager/public/cpp/lib/view_manager_client_impl.h"
 
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/public/cpp/application/connect.h"
 #include "mojo/public/cpp/application/service_provider_impl.h"
 #include "mojo/public/interfaces/application/service_provider.mojom.h"
@@ skipping 224 matching lines @@
   DCHECK(service);
   service_ = service.Pass();
 }
 ////////////////////////////////////////////////////////////////////////////////
 // ViewManagerClientImpl, ViewManager implementation:
 
 Id ViewManagerClientImpl::CreateViewOnServer() {
   DCHECK(service_);
   const Id view_id = MakeTransportId(connection_id_, ++next_id_);
   service_->CreateView(view_id, [this](ErrorCode code) {
-    OnActionCompleted(code == ERROR_CODE_NONE);
+    OnActionCompleted(code == ErrorCode::NONE);
   });
   return view_id;
 }
 
 const std::string& ViewManagerClientImpl::GetEmbedderURL() const {
   return creator_url_;
 }
 
 View* ViewManagerClientImpl::GetRoot() {
   return root_;
@@ skipping 241 matching lines @@
 void ViewManagerClientImpl::OnActionCompleted(bool success) {
   if (!change_acked_callback_.is_null())
     change_acked_callback_.Run();
 }
 
 Callback<void(bool)> ViewManagerClientImpl::ActionCompletedCallback() {
   return [this](bool success) { OnActionCompleted(success); };
 }
 
 }  // namespace mojo