Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/bound_closure_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import "dart:_js_helper";
-import "package:expect/expect.dart";
+import 'native_testing.dart';
 
 // Test calling convention of property extraction closures.
 
 class AA {
   bar(a, [b = 'A']) => 'AA.bar($a, $b)'; // bar is plain dart convention.
   foo(a, [b = 'A']) => 'AA.foo($a, $b)'; // foo has interceptor convention.
 }
 
 @Native("BB")
 class BB {
@@ skipping 18 matching lines @@
 };
 
 function CC() {}
 CC.prototype.foo = function(u, v) {
   return 'CC.foo(' + u + ', ' + v + ')';
 };
 
 makeBB = function(){return new BB;};
 makeCC = function(){return new CC;};
 inscrutable = function(a){return a;};
+
+self.nativeConstructor(BB);
+self.nativeConstructor(CC);
 """;
 
 main() {
+  nativeTesting();
   setup();
   var a = inscrutable(new AA());
   var b = inscrutable(makeBB());
   var c = inscrutable(makeCC)();
 
   Expect.equals('AA.bar(1, A)', inscrutable(a).bar(1));
   Expect.equals('AA.bar(2, 3)', inscrutable(a).bar(2, 3));
 
   Expect.equals('AA.foo(1, A)', inscrutable(a).foo(1));
   Expect.equals('AA.foo(2, 3)', inscrutable(a).foo(2, 3));
@@ skipping 14 matching lines @@
 
   Expect.equals('AA.foo(1, A)', afoo(1));
   Expect.equals('AA.foo(2, 3)', afoo(2, 3));
 
   Expect.equals('BB.foo(1, B)', bfoo(1));
   Expect.equals('BB.foo(2, 3)', bfoo(2, 3));
 
   Expect.equals('CC.foo(1, C)', cfoo(1));
   Expect.equals('CC.foo(2, 3)', cfoo(2, 3));
 }