Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/abstract_class_test.dart

Index: tests/compiler/dart2js_native/abstract_class_test.dart
diff --git a/tests/compiler/dart2js_native/abstract_class_test.dart b/tests/compiler/dart2js_native/abstract_class_test.dart
index 18e0af3723467249e10c4e60932a04ee51363df6..d90fe2ecfeaa94e0e75c3f0a69404c6122d1868a 100644
--- a/tests/compiler/dart2js_native/abstract_class_test.dart
+++ b/tests/compiler/dart2js_native/abstract_class_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";
 
 // Native classes can have subclasses that are not declared to the program.  The
 // subclasses are indistinguishable from the base class.  This means that
@@ -29,17 +28,17 @@ function B(){}
 B.prototype.foo = function() { return 'B.foo'; };
 makeA = function(){return new A};
 makeB = function(){return new B};
+self.nativeConstructor(A);
+self.nativeConstructor(B);
 """;
 
-var inscrutable;
 main() {
+  nativeTesting();
   setup();
-  inscrutable = (x) => x;
-  inscrutable = inscrutable(inscrutable);
 
   var a = makeA();
   var b = makeB();
-  var c = inscrutable(new C());
+  var c = confuse(new C());
 
   Expect.isTrue(a is A);
   Expect.isFalse(b is A);