Add runtime function for string to array conversion.

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 512 matching lines @@
   if (%_ArgumentsLength() === 0) {
     return [subject];
   }
 
   var length = subject.length;
   if (!IS_REGEXP(separator)) {
     separator = TO_STRING_INLINE(separator);
     var separator_length = separator.length;
 
     // If the separator string is empty then return the elements in the subject.
-    if (separator_length === 0) {
-      var result = $Array(length);
-      for (var i = 0; i < length; i++) result[i] = subject[i];
-      return result;
-    }
+    if (separator_length === 0) return %StringToArray(subject);
 
     var result = [];
     var start_index = 0;
     var index;
     while (true) {
       if (start_index + separator_length > length ||
           (index = %StringIndexOf(subject, separator, start_index)) === -1) {
         result.push(SubString(subject, start_index, length));
         break;
       }
@@ skipping 356 matching lines @@
     "small", StringSmall,
     "strike", StringStrike,
     "sub", StringSub,
     "sup", StringSup,
     "toJSON", StringToJSON
   ));
 }
 
 
 SetupString();