Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/native_class_avoids_hidden_name_frog_test.dart

 // Copyright (c) 2011, 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 "dart:_js_helper";
+import "package:expect/expect.dart";
 
 // Test that hidden native class names are not used by generated code.
 
 @Native("BB")
 class AA {
   get name => 'AA';
   static AA create() => makeA();
 }
 
 @Native("CC")
@@ skipping 17 matching lines @@
 BB = null;
 CC = null;
 """;
 
 void setup2() native """
 // This code is all inside 'setup' and so not accesible from the global scope.
 function BB(){}
 function CC(){}
 makeA = function(){return new BB};  // AA is native "BB"
 makeB = function(){return new CC};  // BB is native "CC"
-self.nativeConstructor(BB);
-self.nativeConstructor(CC);
 """;
 
+int inscrutable(int x) => x == 0 ? 0 : x | inscrutable(x & (x - 1));
+
 main() {
-  nativeTesting();
   setup1();
   setup2();
 
-  var a = confuse(AA.create());
-  var b = confuse(BB.create());
-  var c = confuse(CC.create());
+  var things = [AA.create(), BB.create(), CC.create()];
+  var a = things[inscrutable(0)];
+  var b = things[inscrutable(1)];
+  var c = things[inscrutable(2)];
 
   Expect.equals('AA', a.name);
   Expect.equals('BB', b.name);
   Expect.equals('CC', c.name);
 }