Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_no_such_method_exception3_frog_test.dart

 // Copyright (c) 2012, 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:mirrors" show reflect;
-import "dart:_js_helper";
-import "package:expect/expect.dart";
+import "native_testing.dart";
 
 class GetName {
   foo(x, y, [z]) => "foo";
 }
 
 String getName(im) => reflect(new GetName()).delegate(im);
 
 @Native("A")
 class A {
   bar() => 42;
 }
 
 @Native("B")
 class B {
   foo() => 42;
 }
 
 class C {
   static create() => new C();
   noSuchMethod(x) => "${getName(x)}:${x.positionalArguments}";
 }
 
 makeA() native ;
 
 setup() native """
   function A() {}
   makeA = function() { return new A; }
+
+  self.nativeConstructor(A);
 """;
 
 main() {
+  nativeTesting();
   setup();
   var a = makeA();
   a.bar();
   var exception;
   try {
     a.foo();
   } on NoSuchMethodError catch (e) {
     exception = e;
   }
   Expect.isNotNull(exception);
   var c = C.create();
   Expect.equals("foo:[1, 2]", c.foo(1, 2));
   Expect.equals("foo:[3, 4, 5]", c.foo(3, 4, 5));
 }