Fix regression in JSON serialization of RegExps.

src/string.js

 // Copyright 2006-2009 the V8 project authors. 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
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 857 matching lines @@
   }
 }
 
 
 ReplaceResultBuilder.prototype.generate = function() {
   var elements = this.elements;
   return %StringBuilderConcat(elements, elements.length, this.special_string);
 }
 
 
-function StringToJSON(key) {
-  return CheckJSONPrimitive(this.valueOf());
-}
-
-
 // -------------------------------------------------------------------
 
 function SetupString() {
   // Setup the constructor property on the String prototype object.
   %SetProperty($String.prototype, "constructor", $String, DONT_ENUM);
 
 
   // Setup the non-enumerable functions on the String object.
   InstallFunctions($String, DONT_ENUM, $Array(
     "fromCharCode", StringFromCharCode
@@ skipping 29 matching lines @@
     "fontcolor", StringFontcolor,
     "fontsize", StringFontsize,
     "big", StringBig,
     "blink", StringBlink,
     "bold", StringBold,
     "fixed", StringFixed,
     "italics", StringItalics,
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
-    "sup", StringSup,
-    "toJSON", StringToJSON
+    "sup", StringSup
   ));
 }
 
 
 SetupString();