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

chrome/browser/speech/extension_api/tts_extension_api_platform.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_PLATFORM_H_
 #define CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_EXTENSION_API_PLATFORM_H_
 
 #include <string>
 
 #include "chrome/browser/speech/extension_api/tts_extension_api_controller.h"
@@ skipping 16 matching lines @@
   // before speaking again.
   virtual bool Speak(
       int utterance_id,
       const std::string& utterance,
       const std::string& lang,
       const UtteranceContinuousParameters& params) = 0;
 
   // Stop speaking immediately and return true on success.
   virtual bool StopSpeaking() = 0;
 
+  // Returns whether any speech is on going.
+  virtual bool IsSpeaking() = 0;
+
   // Return true if this platform implementation will fire the given event.
   // All platform implementations must fire the TTS_EVENT_END event at a
   // minimum.
   virtual bool SendsEvent(TtsEventType event_type) = 0;
 
   // Return the gender of the voice, should be either "male" or "female"
   // if known, otherwise the empty string.
   virtual std::string gender();
 
   virtual std::string error();
   virtual void clear_error();
   virtual void set_error(const std::string& error);
 
  protected:
   ExtensionTtsPlatformImpl() {}
   virtual ~ExtensionTtsPlatformImpl() {}
 
   std::string error_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionTtsPlatformImpl);
 };
 
 #endif  // CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_EXTENSION_API_PLATFORM_H_