Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart

Index: tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart b/tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart
index d01b4ffbb6e636b5e9a50f3cea2a2b97951965e8..49c7bfdfc5fa715d219abd5dab2ce1404e117c9f 100644
--- a/tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_class_inheritance2_frog_test.dart
@@ -2,8 +2,7 @@
 // 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
@@ -59,9 +58,15 @@ makeA = function(){return new A};
 makeB = function(){return new B};
 makeC = function(){return new C};
 makeD = function(){return new D};
+
+self.nativeConstructor(A);
+self.nativeConstructor(B);
+self.nativeConstructor(C);
+self.nativeConstructor(D);
 """;
 
 main() {
+  nativeTesting();
   setup();
 
   var a = makeA();