Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_method_rename2_frog_test.dart

 // Copyright (c) 2011, 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.
 
 // Test the feature where the native string declares the native method's name.
 
-import "package:expect/expect.dart";
-import 'dart:_js_helper' show Native, JSName;
+import "native_testing.dart";
 
 @Native("A")
 class A {
   @JSName('fooA')
   int foo() native ;
 }
 
 @Native("B")
 class B extends A {
   @JSName('fooB')
@@ skipping 16 matching lines @@
   }
 }
 function A(){}
 A.prototype.fooA = function(){return 100;};
 function B(){}
 inherits(B, A);
 B.prototype.fooB = function(){return 200;};
 
 makeA = function(){return new A};
 makeB = function(){return new B};
+
+self.nativeConstructor(A);
+self.nativeConstructor(B);
 """;
 
 testDynamic() {
   var things = [makeA(), makeB()];
   var a = things[0];
   var b = things[1];
 
   Expect.equals(100, a.foo());
   Expect.equals(200, b.foo());
 
@@ skipping 14 matching lines @@
 
 testTyped() {
   A a = makeA();
   B b = makeB();
 
   Expect.equals(100, a.foo());
   Expect.equals(200, b.foo());
 }
 
 main() {
+  nativeTesting();
   setup();
 
   testDynamic();
   testTyped();
 }
 
 expectNoSuchMethod(action, note) {
   bool caught = false;
   try {
     action();
   } catch (ex) {
     caught = true;
     Expect.isTrue(ex is NoSuchMethodError, note);
   }
   Expect.isTrue(caught, note);
 }