Support onvoiceschanged for extension-based tts engines.

chrome/browser/speech/tts_extension_loader_chromeos.h

-// 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.
-
-#ifndef CHROME_BROWSER_SPEECH_TTS_EXTENSION_LOADER_CHROMEOS_H_
-#define CHROME_BROWSER_SPEECH_TTS_EXTENSION_LOADER_CHROMEOS_H_
-
-#include "components/keyed_service/core/keyed_service.h"
-#include "extensions/browser/event_router.h"
-
-class Profile;
-
-// Profile-keyed class that loads a built-in TTS component extension
-// into a given profile on Chrome OS.
-class TtsExtensionLoaderChromeOs : public KeyedService,
-                                   public extensions::EventRouter::Observer {
- public:
-  static TtsExtensionLoaderChromeOs* GetInstance(Profile* profile);
-
-  // Returns true if the extension was not previously loaded and is now
-  // loading. This class will call
-  // ExtensionTtsController::RetrySpeakingQueuedUtterances when the
-  // extension finishes loading.
-  bool LoadTtsExtension();
-
-  // Implementation of KeyedService.
-  virtual void Shutdown() OVERRIDE;
-
-  // Implementation of extensions::EventRouter::Observer.
-  virtual void OnListenerAdded(const extensions::EventListenerInfo& details)
-      OVERRIDE;
-
- private:
-  // The state of TTS for this profile.
-  enum TtsState {
-    TTS_NOT_LOADED,
-    TTS_LOAD_REQUESTED,
-    TTS_LOADING,
-    TTS_LOADED
-  };
-
-  explicit TtsExtensionLoaderChromeOs(Profile* profile);
-  virtual ~TtsExtensionLoaderChromeOs() {}
-
-  bool IsTtsLoadedInThisProfile();
-
-  Profile* profile_;
-  TtsState tts_state_;
-
-  friend class TtsExtensionLoaderChromeOsFactory;
-
-  DISALLOW_COPY_AND_ASSIGN(TtsExtensionLoaderChromeOs);
-};
-
-#endif  // CHROME_BROWSER_SPEECH_TTS_EXTENSION_LOADER_CHROMEOS_H_