Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/issue9182_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.
 
 // Regression test for Issue 9182.  The generative constructor body function
 // should not have the interceptor calling convention.
 
-import "dart:_js_helper";
-import "package:expect/expect.dart";
+import "native_testing.dart";
 
 @Native("A")
 class Foo {
   factory Foo() => makeA();
   // Ensure the instance method 'Bar' uses interceptor convention.
   Bar() => 123;
 }
 
 class Bar {
   var _x, _y;
   // Generative constructor with body, having the same name as interceptor
   // convention instance member.
   Bar(x, y) {
     _x = x;
     _y = y;
   }
 }
 
 void setup() native r"""
 function A(){}
 makeA = function() { return new A; };
+self.nativeConstructor(A);
 """;
 
 makeA() native ;
 
 main() {
+  nativeTesting();
   setup();
 
-  var things = [new Foo(), new Bar(30, 40)];
-  var foo = things[0];
-  var bar = things[1];
+  var foo = confuse(new Foo());
+  var bar = confuse(new Bar(30, 40));
 
   Expect.equals(123, foo.Bar()); // Ensure that Foo.Bar is used.
 
   Expect.equals(30, bar._x);
   Expect.equals(40, bar._y);
 }