Uses a system-wide notion of isSpeaking in the Mac extension TTS api.

chrome/browser/speech/extension_api/tts_extension_api_controller.h

 // Copyright (c) 2012 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_EXTENSION_API_CONTROLLER_H_
 #define CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_EXTENSION_API_CONTROLLER_H_
 
 #include <queue>
 #include <set>
 #include <string>
@@ skipping 173 matching lines @@
 
 // Singleton class that manages text-to-speech for the TTS and TTS engine
 // extension APIs, maintaining a queue of pending utterances and keeping
 // track of all state.
 class ExtensionTtsController {
  public:
   // Get the single instance of this class.
   static ExtensionTtsController* GetInstance();
 
   // Returns true if we're currently speaking an utterance.
-  bool IsSpeaking() const;
+  bool IsSpeaking();
 
   // Speak the given utterance. If the utterance's can_enqueue flag is true
   // and another utterance is in progress, adds it to the end of the queue.
   // Otherwise, interrupts any current utterance and speaks this one
   // immediately.
   void SpeakOrEnqueue(Utterance* utterance);
 
   // Stop all utterances and flush the queue.
   void Stop();
 
@@ skipping 45 matching lines @@
   std::queue<Utterance*> utterance_queue_;
 
   // A pointer to the platform implementation of text-to-speech, for
   // dependency injection.
   ExtensionTtsPlatformImpl* platform_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionTtsController);
 };
 
 #endif  // CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_EXTENSION_API_CONTROLLER_H_