Aviod double checking IS_STRING when joining arrays.

src/v8natives.js

 // Copyright 2006-2008 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 1138 matching lines @@
   return result;
 }
 
 
 function NewFunction(arg1) {  // length == 1
   var n = %_ArgumentsLength();
   var p = '';
   if (n > 1) {
     p = new $Array(n - 1);
     for (var i = 0; i < n - 1; i++) p[i] = %_Arguments(i);
-    p = Join(p, n - 1, ',', ToString);
+    p = Join(p, n - 1, ',', NonStringToString);
     // If the formal parameters string include ) - an illegal
     // character - it may make the combined function expression
     // compile. We avoid this problem by checking for this early on.
     if (p.indexOf(')') != -1) throw MakeSyntaxError('unable_to_parse',[]);
   }
   var body = (n > 0) ? ToString(%_Arguments(n - 1)) : '';
   var source = '(function(' + p + ') {\n' + body + '\n})';
 
   // The call to SetNewFunctionAttributes will ensure the prototype
   // property of the resulting function is enumerable (ECMA262, 15.3.5.2).
   var f = %CompileString(source)();
   %FunctionSetName(f, "anonymous");
   return %SetNewFunctionAttributes(f);
 }
 
 %SetCode($Function, NewFunction);
 
 // ----------------------------------------------------------------------------
 
 function SetupFunction() {
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "bind", FunctionBind,
     "toString", FunctionToString
   ));
 }
 
 SetupFunction();