Don't forget to call RemoveObserver when TtsDispatcher is destroyed.

chrome/renderer/tts_dispatcher.cc

 // Copyright (c) 2013 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 "chrome/renderer/tts_dispatcher.h"
 
 #include "base/basictypes.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/common/tts_messages.h"
 #include "chrome/common/tts_utterance_request.h"
@@ skipping 12 matching lines @@
 using WebKit::WebVector;
 
 int TtsDispatcher::next_utterance_id_ = 1;
 
 TtsDispatcher::TtsDispatcher(WebSpeechSynthesizerClient* client)
     : synthesizer_client_(client) {
   RenderThread::Get()->AddObserver(this);
 }
 
 TtsDispatcher::~TtsDispatcher() {
+  RenderThread::Get()->RemoveObserver(this);
 }
 
 bool TtsDispatcher::OnControlMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(TtsDispatcher, message)
     IPC_MESSAGE_HANDLER(TtsMsg_SetVoiceList, OnSetVoiceList)
     IPC_MESSAGE_HANDLER(TtsMsg_DidStartSpeaking, OnDidStartSpeaking)
     IPC_MESSAGE_HANDLER(TtsMsg_DidFinishSpeaking, OnDidFinishSpeaking)
     IPC_MESSAGE_HANDLER(TtsMsg_DidPauseSpeaking, OnDidPauseSpeaking)
     IPC_MESSAGE_HANDLER(TtsMsg_DidResumeSpeaking, OnDidResumeSpeaking)
@@ skipping 146 matching lines @@
 void TtsDispatcher::OnSpeakingErrorOccurred(int utterance_id,
                                             const std::string& error_message) {
   WebSpeechSynthesisUtterance utterance = FindUtterance(utterance_id);
   if (utterance.isNull())
     return;
 
   // The web speech API doesn't support an error message.
   synthesizer_client_->speakingErrorOccurred(utterance);
   utterance_id_map_.erase(utterance_id);
 }