Mojo C++ bindings: switch part of the services/ui/public/interfaces mojom target to use STL types.

services/ui/ws/user_id_tracker.cc

 // Copyright 2016 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 "services/ui/ws/user_id_tracker.h"
 
 #include "services/service_manager/public/interfaces/connector.mojom.h"
 #include "services/ui/ws/user_id_tracker_observer.h"
 
 namespace ui {
@@ skipping 43 matching lines @@
 }
 
 void UserIdTracker::RemoveObserver(UserIdTrackerObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
 void UserIdTracker::Bind(mojom::UserAccessManagerRequest request) {
   bindings_.AddBinding(this, std::move(request));
 }
 
-void UserIdTracker::SetActiveUser(const mojo::String& user_id) {
+void UserIdTracker::SetActiveUser(const std::string& user_id) {
   if (!IsValidUserId(user_id))
     AddUserId(user_id);
   SetActiveUserId(user_id);
 }
 
 }  // namespace ws
 }  // namespace ui