Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/jsobject_test.dart

Index: tests/compiler/dart2js_native/jsobject_test.dart
diff --git a/tests/compiler/dart2js_native/jsobject_test.dart b/tests/compiler/dart2js_native/jsobject_test.dart
index f7a92f942d668780e49242e0c6915f241d2e4801..7f31dd1220fe85742cc67b49e669726f1575880b 100644
--- a/tests/compiler/dart2js_native/jsobject_test.dart
+++ b/tests/compiler/dart2js_native/jsobject_test.dart
@@ -2,8 +2,8 @@
 // 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 "package:expect/expect.dart";
-import 'dart:_js_helper' show Native, Creates, setNativeSubclassDispatchRecord;
+import 'native_testing.dart';
+import 'dart:_js_helper' show setNativeSubclassDispatchRecord;
 import 'dart:_interceptors'
     show
         JSObject, // The interface, which may be re-exported by a
@@ -32,6 +32,8 @@ makeB = function(){return new BB();};
 
 function QQ(){}
 makeQ = function(){return new QQ();};
+
+self.nativeConstructor(QQ);
 """;
 
 class Is<T> {
@@ -93,6 +95,7 @@ dynamic_test() {
 }
 
 main() {
+  nativeTesting();
   setup();
 
   dynamic_test();