Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_class_inheritance1_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.
 
-import "dart:_js_helper";
-import "package:expect/expect.dart";
+import "native_testing.dart";
 
 // Test to see if resolving a hidden native class's method interferes with
 // subsequent resolving the subclass's method.  This might happen if the
 // superclass caches the method in the prototype, so shadowing the dispatcher
 // stored on Object.prototype.
 
 // Version 1: It might be possible to call foo directly.
 @Native("A1")
 class A1 {
   foo() native ;
@@ skipping 43 matching lines @@
 makeB1 = function(){return new B1};
 
 function A2(){}
 function B2(){}
 inherits(B2, A2);
 A2.prototype.foo = function(a){return a + 10000;}
 B2.prototype.foo = function(z){return z + 20000;}
 
 makeA2 = function(){return new A2};
 makeB2 = function(){return new B2};
+
+self.nativeConstructor(A1);
+self.nativeConstructor(A2);
+self.nativeConstructor(B1);
+self.nativeConstructor(B2);
 """;
 
 main() {
+  nativeTesting();
   setup();
 
   var a1 = makeA1();
   var b1 = makeB1();
   Expect.equals(100, a1.foo());
   Expect.equals(200, b1.foo());
 
   var a2 = makeA2();
   var b2 = makeB2();
   Expect.equals(10000 + 99, a2.foo());
@@ skipping 14 matching lines @@
   caught = false;
   try {
     var x = 123;
     x.foo(20);
   } catch (ex) {
     caught = true;
     Expect.isTrue(ex is NoSuchMethodError);
   }
   Expect.isTrue(caught, "x.foo(20) should throw");
 }