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

chrome/browser/speech/extension_api/tts_extension_api_mac.mm

 // 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.
 
 #include <string>
 
 #include "base/mac/cocoa_protocols.h"
 #include "base/memory/scoped_nsobject.h"
 #include "base/memory/singleton.h"
 #include "base/sys_string_conversions.h"
@@ skipping 111 matching lines @@
 
 bool ExtensionTtsPlatformImplMac::StopSpeaking() {
   if (speech_synthesizer_.get()) {
     [speech_synthesizer_ stopSpeaking];
     speech_synthesizer_.reset(nil);
   }
   return true;
 }
 
 bool ExtensionTtsPlatformImplMac::IsSpeaking() {
-  // Note: this is OK even if speech_synthesizer_ is nil, it will return false.
-  return [speech_synthesizer_ isSpeaking];
+  return [NSSpeechSynthesizer isAnyApplicationSpeaking];
 }
 
 bool ExtensionTtsPlatformImplMac::SendsEvent(TtsEventType event_type) {
   return (event_type == TTS_EVENT_START ||
           event_type == TTS_EVENT_END ||
           event_type == TTS_EVENT_WORD ||
           event_type == TTS_EVENT_ERROR);
 }
 
 void ExtensionTtsPlatformImplMac::OnSpeechEvent(
@@ skipping 58 matching lines @@
 - (void)speechSynthesizer:(NSSpeechSynthesizer*)sender
  didEncounterErrorAtIndex:(NSUInteger)character_index
                  ofString:(NSString*)string
                   message:(NSString*)message {
   std::string message_utf8 = base::SysNSStringToUTF8(message);
   ttsImplMac_->OnSpeechEvent(sender, TTS_EVENT_ERROR, character_index,
       message_utf8);
 }
 
 @end