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

services/ui/ws/window_server_test_impl.h

 // 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.
 
 #ifndef SERVICES_UI_WS_WINDOW_SERVER_TEST_IMPL_H_
 #define SERVICES_UI_WS_WINDOW_SERVER_TEST_IMPL_H_
 
 #include "services/ui/public/interfaces/window_server_test.mojom.h"
 
 namespace ui {
 namespace ws {
 
 class ServerWindow;
 class WindowServer;
 class WindowTree;
 struct WindowId;
 
 class WindowServerTestImpl : public mojom::WindowServerTest {
  public:
   explicit WindowServerTestImpl(WindowServer* server);
   ~WindowServerTestImpl() override;
 
  private:
   void OnWindowPaint(const std::string& name,
                      const EnsureClientHasDrawnWindowCallback& cb,
                      ServerWindow* window);
 
   // mojom::WindowServerTest:
   void EnsureClientHasDrawnWindow(
-      const mojo::String& client_name,
+      const std::string& client_name,
       const EnsureClientHasDrawnWindowCallback& callback) override;
 
   WindowServer* window_server_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowServerTestImpl);
 };
 
 }  // namespace ws
 }  // namespace ui
 
 #endif  // SERVICES_UI_WS_WINDOW_SERVER_TEST_IMPL_H_