Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/runtimetype_test.dart

Index: tests/compiler/dart2js_native/runtimetype_test.dart
diff --git a/tests/compiler/dart2js_native/runtimetype_test.dart b/tests/compiler/dart2js_native/runtimetype_test.dart
index 4667eca8d8808d984ee3f5faa516c30ea0e2914e..babdc1168d21092f7fb8b2b78f06f5e249be43cc 100644
--- a/tests/compiler/dart2js_native/runtimetype_test.dart
+++ b/tests/compiler/dart2js_native/runtimetype_test.dart
@@ -2,9 +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 "package:expect/expect.dart";
-import "dart:_js_helper";
-import 'dart:_foreign_helper' show JS;
+import 'native_testing.dart';
 
 // Test to see runtimeType works on native classes and does not use the native
 // constructor name.
@@ -33,6 +31,9 @@ inherits(TAGY, TAGX);
 
 makeA = function(){return new TAGX};
 makeB = function(){return new TAGY};
+
+self.nativeConstructor(TAGX);
+self.nativeConstructor(TAGY);
 """;
 
 testDynamicContext() {
@@ -58,6 +59,7 @@ testStaticContext() {
 }
 
 main() {
+  nativeTesting();
   setup();
 
   testDynamicContext();