Hide Symbol implementation in a closure.

src/string.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var $stringCharAt;
 var $stringIndexOf;
 var $stringSubstring;
 
 (function() {
 
 %CheckIsBootstrapping();
 
 var GlobalArray = global.Array;
 var GlobalRegExp = global.RegExp;
 var GlobalString = global.String;
 
 //-------------------------------------------------------------------
 
 function StringConstructor(x) {
   if (%_ArgumentsLength() == 0) x = '';
   if (%_IsConstructCall()) {
     %_SetValueOf(this, TO_STRING_INLINE(x));
   } else {
     return IS_SYMBOL(x) ?
-        %_CallFunction(x, SymbolToString) : TO_STRING_INLINE(x);
+        %_CallFunction(x, $symbolToString) : TO_STRING_INLINE(x);
   }
 }
 
 
 // ECMA-262 section 15.5.4.2
 function StringToString() {
   if (!IS_STRING(this) && !IS_STRING_WRAPPER(this)) {
     throw new $TypeError('String.prototype.toString is not generic');
   }
   return %_ValueOf(this);
@@ skipping 948 matching lines @@
   "strike", StringStrike,
   "sub", StringSub,
   "sup", StringSup
 ));
 
 $stringCharAt = StringCharAt;
 $stringIndexOf = StringIndexOfJS;
 $stringSubstring = StringSubstring;
 
 })();