Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_field_invocation5_test.dart

Index: tests/compiler/dart2js_native/native_field_invocation5_test.dart
diff --git a/tests/compiler/dart2js_native/native_field_invocation5_test.dart b/tests/compiler/dart2js_native/native_field_invocation5_test.dart
index abc60aad90a0c2bd48f0b1d0d87e85f3c5a44dcf..5c3ff7b6e05625c8ff91f4c76ec14f725cb14a1d 100644
--- a/tests/compiler/dart2js_native/native_field_invocation5_test.dart
+++ b/tests/compiler/dart2js_native/native_field_invocation5_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";
 
 makeCC() native ;
 nativeFirst(x, y) native ;
@@ -12,6 +11,7 @@ void setup() native """
 function CC() {}
 makeCC = function() { return new CC; }
 nativeFirst = function(x, y) { return x; }
+self.nativeConstructor(CC);
 """;
 
 class C {
@@ -38,6 +38,7 @@ wrap(cb) {
 }
 
 main() {
+  nativeTesting();
   setup();
   var c = makeCC();
   c.init();