Extend PlatformSpeechSynthesizerMock with an utterance queue.

Source/modules/speech/DOMWindowSpeechSynthesis.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 52 matching lines @@
 // static
 SpeechSynthesis* DOMWindowSpeechSynthesis::speechSynthesis(DOMWindow& window)
 {
     return DOMWindowSpeechSynthesis::from(toLocalDOMWindow(window)).speechSynthesis();
 }
 
 SpeechSynthesis* DOMWindowSpeechSynthesis::speechSynthesis()
 {
     if (!m_speechSynthesis && frame())
         m_speechSynthesis = SpeechSynthesis::create(frame()->domWindow()->executionContext());
-    return m_speechSynthesis.get();
+    return m_speechSynthesis;
 }
 
 void DOMWindowSpeechSynthesis::trace(Visitor* visitor)
 {
     visitor->trace(m_speechSynthesis);
     WillBeHeapSupplement<LocalDOMWindow>::trace(visitor);
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink