Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/super_property_test.dart

 // Copyright (c) 2013, 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";
 
 // Tests super setter where the HInvokeSuper is using interceptor aka
 // explicit-receiver calling convention.
 
 @Native("A")
 class A {
   var foo;
   get_foo() => foo;
   set bar(value) => foo = value;
 }
@@ skipping 23 matching lines @@
 
 makeA() native ;
 makeB() native ;
 
 void setup() native """
 // This code is all inside 'setup' and so not accesible from the global scope.
 function A(){}
 function B(){}
 makeA = function(){return new A};
 makeB = function(){return new B};
+self.nativeConstructor(A);
+self.nativeConstructor(B);
 """;
 
 testThing(a) {
   a.foo = 123;
   Expect.equals(123, a.foo);
   Expect.equals(123, a.get_foo());
 
   a.bar = 234;
   Expect.equals(234, a.foo);
   Expect.equals(234, a.get_foo());
 }
 
 main() {
+  nativeTesting();
   setup();
   var things = [makeA(), makeB(), new C(), new D()];
   var test = testThing;
   test(things[0]);
   test(things[1]);
   test(things[2]);
   test(things[3]);
 }