Support onvoiceschanged for extension-based tts engines.

chrome/browser/speech/extension_api/tts_engine_extension_observer.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_EXTENSION_API_TTS_ENGINE_EXTENSION_OBSERVER_H_
+#define CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_ENGINE_EXTENSION_OBSERVER_H_
+
+#include "base/scoped_observer.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "extensions/browser/event_router.h"
+#include "extensions/browser/extension_registry.h"
+#include "extensions/browser/extension_registry_observer.h"
+
+class Profile;
+
+// Profile-keyed class that observes the extension registry to determine load of
+// extension-based tts engines.
+class TtsEngineExtensionObserver
+    : public KeyedService,
+      public extensions::EventRouter::Observer,
+      public extensions::ExtensionRegistryObserver {
+ public:
+  static TtsEngineExtensionObserver* GetInstance(Profile* profile);
+
+  // Returns if this observer saw the given extension load. Adds |extension_id|
+  // as loaded immediately if |update| is set to true.
+  bool SawExtensionLoad(const std::string& extension_id, bool update);
+
+  // Implementation of KeyedService.
+  virtual void Shutdown() OVERRIDE;
+
+  // Implementation of extensions::EventRouter::Observer.
+  virtual void OnListenerAdded(
+      const extensions::EventListenerInfo& details) OVERRIDE;
+
+  // extensions::ExtensionRegistryObserver overrides.
+  virtual void OnExtensionUnloaded(
+      content::BrowserContext* browser_context,
+      const extensions::Extension* extension,
+      extensions::UnloadedExtensionInfo::Reason reason) OVERRIDE;
+
+ private:
+  explicit TtsEngineExtensionObserver(Profile* profile);
+  virtual ~TtsEngineExtensionObserver();
+
+  bool IsLoadedTtsEngine(const std::string& extension_id);
+
+  ScopedObserver<extensions::ExtensionRegistry,
+                 extensions::ExtensionRegistryObserver>
+      extension_registry_observer_;
+
+  Profile* profile_;
+
+  bool saw_tts_engine_added_;
+
+  std::set<std::string> engine_extension_ids_;
+
+  friend class TtsEngineExtensionObserverFactory;
+
+  DISALLOW_COPY_AND_ASSIGN(TtsEngineExtensionObserver);
+};
+
+#endif  // CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_ENGINE_EXTENSION_OBSERVER_H_