Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_class_inheritance3_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 to noSuchMethod
 // interferes with subsequent resolving of the method.  This might happen if the
 // noSuchMethod is cached on Object.prototype.
 
 @Native("A1")
 class A1 {}
 
 @Native("B1")
 class B1 extends A1 {}
@@ skipping 35 matching lines @@
 
 function A2(){}
 function B2(){}
 inherits(B2, A2);
 A2.prototype.foo = function(a){return 'A2.foo(' + a  + ')';}
 
 makeA2 = function(){return new A2};
 makeB2 = function(){return new B2};
 
 makeObject = function(){return new Object};
+
+self.nativeConstructor(A1);
+self.nativeConstructor(A2);
+self.nativeConstructor(B1);
+self.nativeConstructor(B2);
 """;
 
 main() {
+  nativeTesting();
   setup();
 
   var a1 = makeA1();
   var b1 = makeB1();
   var ob = makeObject();
 
   // Does calling missing methods in one tree of inheritance forest affect other
   // trees?
   expectNoSuchMethod(() => b1.foo(), 'b1.foo()');
   expectNoSuchMethod(() => a1.foo(), 'a1.foo()');
@@ skipping 14 matching lines @@
 expectNoSuchMethod(action, note) {
   bool caught = false;
   try {
     action();
   } catch (ex) {
     caught = true;
     Expect.isTrue(ex is NoSuchMethodError, note);
   }
   Expect.isTrue(caught, note);
 }