Use import/export for more functions (instead of js builtins object).

src/js/messages.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 $errorToString;
 var MakeError;
 var MakeEvalError;
 var MakeRangeError;
 var MakeReferenceError;
 var MakeSyntaxError;
 var MakeTypeError;
 var MakeURIError;
 
 (function(global, utils) {
 
@@ skipping 958 matching lines @@
   if (!IS_SPEC_OBJECT(this)) {
     throw MakeTypeError(kCalledOnNonObject, "Error.prototype.toString");
   }
 
   return %ErrorToStringRT(this);
 }
 
 utils.InstallFunctions(GlobalError.prototype, DONT_ENUM,
                        ['toString', ErrorToString]);
 
-$errorToString = ErrorToString;
-
 MakeError = function(type, arg0, arg1, arg2) {
   return MakeGenericError(GlobalError, type, arg0, arg1, arg2);
 }
 
 MakeRangeError = function(type, arg0, arg1, arg2) {
   return MakeGenericError(GlobalRangeError, type, arg0, arg1, arg2);
 }
 
 MakeSyntaxError = function(type, arg0, arg1, arg2) {
   return MakeGenericError(GlobalSyntaxError, type, arg0, arg1, arg2);
@@ skipping 38 matching lines @@
   "no_side_effect_to_string_fun", NoSideEffectToString,
   "range_error_function", GlobalRangeError,
   "reference_error_function", GlobalReferenceError,
   "stack_overflow_boilerplate", StackOverflowBoilerplate,
   "syntax_error_function", GlobalSyntaxError,
   "to_detail_string_fun", ToDetailString,
   "type_error_function", GlobalTypeError,
   "uri_error_function", GlobalURIError,
 ]);
 
+utils.Export(function(to) {
+  to.ErrorToString = ErrorToString;
 });
+
+});