Switch speech synthesis from compile-flag to runtime-flag.

Source/core/platform/PlatformSpeechSynthesisUtterance.h

 /*
  * Copyright (C) 2013 Apple Computer, Inc.  All rights reserved.
  *
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  * modification, are permitted provided that the following conditions
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 #ifndef PlatformSpeechSynthesisUtterance_h
 #define PlatformSpeechSynthesisUtterance_h
 
-#if ENABLE(SPEECH_SYNTHESIS)
-
 #include "core/platform/PlatformSpeechSynthesisVoice.h"
 #include <wtf/PassRefPtr.h>
 #include <wtf/RefCounted.h>
 #include <wtf/text/WTFString.h>
 
 namespace WebCore {
     
 class PlatformSpeechSynthesisUtteranceClient {
 public:
     // Implement methods as needed.
@@ skipping 40 matching lines @@
     String m_lang;
     RefPtr<PlatformSpeechSynthesisVoice> m_voice;
     float m_volume;
     float m_rate;
     float m_pitch;
     double m_startTime;
 };
     
 } // namespace WebCore
 
-#endif // ENABLE(SPEECH_SYNTHESIS)
-
 #endif // PlatformSpeechSynthesisUtterance_h