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

Source/modules/speech/SpeechSynthesisUtterance.idl

 /*
  * Copyright (C) 2013 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
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 [
-    Conditional=SPEECH_SYNTHESIS,
+    EnabledAtRuntime=speechSynthesis,
     EventTarget,
     CallWith=ScriptExecutionContext,
     Constructor([Default=NullString] optional DOMString text)
 ] interface SpeechSynthesisUtterance {
     attribute DOMString text;
     attribute DOMString lang;
     attribute SpeechSynthesisVoice voice;
     attribute float volume;
     attribute float rate;
     attribute float pitch;
 
     attribute EventListener onstart;
     attribute EventListener onend;
     attribute EventListener onerror;
     attribute EventListener onpause;
     attribute EventListener onresume;
     attribute EventListener onmark;
     attribute EventListener onboundary;
 };