Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/browser_compat_1_prepatched_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.
 
-import "dart:_js_helper";
-import "package:expect/expect.dart";
-//import 'dart:_foreign_helper' show JS;
-//import 'dart:_js_helper' show Creates, setNativeSubclassDispatchRecord;
+import "native_testing.dart";
 
 // Test for dartNativeDispatchHooksTransformer, getTag hook.
 
 @Native("T1A")
 class T1A {}
 
 @Native("T1B")
 class T1B {}
 
 @Native("T1C")
@@ skipping 16 matching lines @@
 
 // Make constructors visible on 'window' for prepatching.
 if (typeof window == "undefined") window = {}
 window.T1A = T1A;
 window.T1CrazyB = T1CrazyB;
 
 makeT1A = function(){return new T1A;};
 makeT1B = function(){return new T1CrazyB;};
 makeT1C = function(){return new T1fakeA;};
 
+self.nativeConstructor(T1A);
+self.nativeConstructor(T1CrazyB);
+self.nativeConstructor(T1fakeA);
+
 var getTagCount = 0;
 getTagCallCount = function() { return getTagCount; }
 
 function transformer1(hooks) {
   var getTag = hooks.getTag;
 
   function getTagNew(obj) {
     ++getTagCount;
 
     // If something looks like a different native type we can check in advance
     // of the default algorithm.
     if (obj instanceof T1fakeA) return "T1C";
 
     var tag = getTag(obj);
 
     // New constructor names can be mapped here.
     if (tag == "T1CrazyB") return "T1B";
 
     return tag;
   }
 
   hooks.getTag = getTagNew;
 }
 
 dartNativeDispatchHooksTransformer = [transformer1];
 ''';
 
-var inscrutable;
-
 main() {
+  nativeTesting();
   setup();
-  inscrutable = (x) => x;
 
   var t1a = makeT1A();
   var t1b = makeT1B();
   var t1c = makeT1C();
 
   Expect.equals(true, t1a is T1A, '$t1a is T1A');
   Expect.equals(true, t1b is T1B, '$t1b is T1B');
   Expect.equals(true, t1c is T1C, '$t1c is T1C');
 
   Expect.equals(2, getTagCallCount());
 
-  Expect.equals(true, inscrutable(t1a) is T1A, '$t1a is T1A');
-  Expect.equals(true, inscrutable(t1b) is T1B, '$t1b is T1B');
-  Expect.equals(true, inscrutable(t1c) is T1C, '$t1c is T1C');
+  Expect.equals(true, confuse(t1a) is T1A, '$t1a is T1A');
+  Expect.equals(true, confuse(t1b) is T1B, '$t1b is T1B');
+  Expect.equals(true, confuse(t1c) is T1C, '$t1c is T1C');
 
   Expect.equals(2, getTagCallCount());
 }