arc: Convert more Mojo types to STL

chrome/browser/chromeos/arc/tts/arc_tts_service.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 CHROME_BROWSER_CHROMEOS_ARC_TTS_ARC_TTS_SERVICE_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_TTS_ARC_TTS_SERVICE_H_
 
+#include <string>
+
 #include "base/macros.h"
 #include "components/arc/arc_service.h"
 #include "components/arc/common/tts.mojom.h"
 #include "components/arc/instance_holder.h"
 #include "mojo/public/cpp/bindings/binding.h"
 
 namespace arc {
 
 class ArcBridgeService;
 
 // Provides text to speech services and events to Chrome OS via Android's text
 // to speech API.
 class ArcTtsService : public ArcService,
                       public InstanceHolder<mojom::TtsInstance>::Observer,
                       public mojom::TtsHost {
  public:
   explicit ArcTtsService(ArcBridgeService* bridge_service);
   ~ArcTtsService() override;
 
   // InstanceHolder<mojom::TtsInstance>::Observer overrides:
   void OnInstanceReady() override;
 
   // mojom::TtsHost overrides:
   void OnTtsEvent(uint32_t id,
                   mojom::TtsEventType event_type,
                   uint32_t char_index,
-                  const mojo::String& error_msg) override;
+                  const std::string& error_msg) override;
 
  private:
   mojo::Binding<mojom::TtsHost> binding_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcTtsService);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_TTS_ARC_TTS_SERVICE_H_