Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/runtimetype_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 'native_testing.dart';
+import "package:expect/expect.dart";
+import "dart:_js_helper";
+import 'dart:_foreign_helper' show JS;
 
 // Test to see runtimeType works on native classes and does not use the native
 // constructor name.
 
 @Native("TAGX")
 class A {}
 
 @Native("TAGY")
 class B extends A {}
 
 makeA() native ;
 makeB() native ;
 
 void setup() native """
 // This code is all inside 'setup' and so not accesible from the global scope.
 function inherits(child, parent) {
   function tmp() {};
   tmp.prototype = parent.prototype;
   child.prototype = new tmp();
   child.prototype.constructor = child;
 }
 
 function TAGX(){}
 function TAGY(){}
 inherits(TAGY, TAGX);
 
 makeA = function(){return new TAGX};
 makeB = function(){return new TAGY};
-
-self.nativeConstructor(TAGX);
-self.nativeConstructor(TAGY);
 """;
 
 testDynamicContext() {
   var a = makeA();
   var b = makeB();
 
   var aT = a.runtimeType;
   var bT = b.runtimeType;
 
   Expect.notEquals('TAGX', '$aT');
   Expect.notEquals('TAGY', '$bT');
 }
 
 testStaticContext() {
   var a = JS('A', '#', makeA()); // Force compiler to know type.
   var b = JS('B', '#', makeB());
 
   var aT = a.runtimeType;
   var bT = b.runtimeType;
 
   Expect.notEquals('TAGX', '$aT');
   Expect.notEquals('TAGY', '$bT');
 }
 
 main() {
-  nativeTesting();
   setup();
 
   testDynamicContext();
   testStaticContext();
 }