Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/native_field_invocation2_test.dart

Index: tests/compiler/dart2js_native/native_field_invocation2_test.dart
diff --git a/tests/compiler/dart2js_native/native_field_invocation2_test.dart b/tests/compiler/dart2js_native/native_field_invocation2_test.dart
index 290a68fa45b6b515bfd5e6870347285e101d6d20..05e2eab6eae435fddffea153b9115f1e45fecdd1 100644
--- a/tests/compiler/dart2js_native/native_field_invocation2_test.dart
+++ b/tests/compiler/dart2js_native/native_field_invocation2_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";
 
 @Native("NNative")
 class NNative {
@@ -11,19 +10,9 @@ class NNative {
 
   var f;
 
-  ClickCounter() {
-    f = wrap(g);
-  }
-
   g(val) => "### $val ###";
 }
 
-nativeId(x) native ;
-
-void setup() native """
-nativeId = function(x) { return x; }
-""";
-
 class ClickCounter {
   var status;
 
@@ -42,6 +31,13 @@ wrap(cb) {
   };
 }
 
+nativeId(x) native ;
+
+void setup() native """
+nativeId = function(x) { return x; }
+""";
+
+
 main() {
   setup();
   // Make sure the ClickCounter class goes through interceptors.