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

Source/core/features.gypi

 #
 # Copyright (C) 2009 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 33 matching lines @@
       'ENABLE_CSS_IMAGE_SET=1',
       'ENABLE_CSS_REGIONS=1',
       'ENABLE_CUSTOM_SCHEME_HANDLER=0',
       'ENABLE_ENCRYPTED_MEDIA=1',
       'ENABLE_JAVASCRIPT_I18N_API=1',
       'ENABLE_MATHML=0',
       'ENABLE_MEDIA_STREAM=<(enable_webrtc)',
       'ENABLE_RESOLUTION_MEDIA_QUERY=0',
       'ENABLE_RUBY=1',
       'ENABLE_SANDBOX=1',
-      'ENABLE_SPEECH_SYNTHESIS=0',
       'ENABLE_SVG=<(enable_svg)',
       'ENABLE_SVG_FONTS=<(enable_svg)',
       'ENABLE_TOUCH_ICON_LOADING=<(enable_touch_icon_loading)',
       'ENABLE_V8_SCRIPT_DEBUG_SERVER=1',
       'ENABLE_VIEWPORT=1',
       'ENABLE_WEBGL=1',
       'ENABLE_XHR_TIMEOUT=0',
       'WTF_USE_BUILTIN_UTF8_CODEC=1',
       # WTF_USE_DYNAMIC_ANNOTATIONS=1 may be defined in build/common.gypi
       # We can't define it here because it should be present only
@@ skipping 89 matching lines @@
         ],
       }],
       ['use_default_render_theme==1', {
         'feature_defines': [
           'ENABLE_DEFAULT_RENDER_THEME=1',
         ],
       }],
     ],
   },
 }