Nuke unused WEBKIT_USING_DART.

Source/WebKit/chromium/public/platform/WebCommon.h

 /*
  * Copyright (C) 2010 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 44 matching lines @@
 #endif
 
 #if !defined(WEBKIT_USING_V8)
     #define WEBKIT_USING_V8 1
 #endif
 
 #if !defined(WEBKIT_USING_JSC)
     #define WEBKIT_USING_JSC 0
 #endif
 
-#if !defined(WEBKIT_USING_DART)
-    #define WEBKIT_USING_DART 1
-#endif
-
 // -----------------------------------------------------------------------------
 // Exported symbols need to be annotated with WEBKIT_EXPORT
 
 #if defined(WEBKIT_DLL)
     #if defined(WIN32)
         #if WEBKIT_IMPLEMENTATION
             #define WEBKIT_EXPORT __declspec(dllexport)
         #else
             #define WEBKIT_EXPORT __declspec(dllimport)
         #endif
@@ skipping 39 matching lines @@
 #else
 #define WEBKIT_ASSERT(assertion) do { \
     if (!(assertion)) \
         failedAssertion(__FILE__, __LINE__, __FUNCTION__, #assertion); \
 } while (0)
 #endif
 
 #define WEBKIT_ASSERT_NOT_REACHED() WEBKIT_ASSERT(0)
 
 #endif