Add native_testing library to mock @Native classes

tests/compiler/dart2js_native/core_type_check_native_test.dart

 // Copyright (c) 2012, 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";
-
-var inscrutable = (int x) => x == 0 ? 0 : x | inscrutable(x & (x - 1));
+import "native_testing.dart";
 
 @Native("A")
 class A {}
 
 @Native("B")
 class B implements Comparable {}
 
 @Native("C")
 class C implements Pattern {}
 
 @Native("D")
 class D implements Pattern, Comparable {}
 
 makeA() native ;
 makeB() native ;
 makeC() native ;
 makeD() native ;
 
 void setup() native """
 function A() {};
 makeA = function() { return new A; }
 function B() {};
 makeB = function() { return new B; }
 function C() {};
 makeC = function() { return new C; }
 function D() {};
 makeD = function() { return new D; }
+
+self.nativeConstructor(A);
+self.nativeConstructor(B);
+self.nativeConstructor(C);
+self.nativeConstructor(D);
 """;
 
 checkTest(value, expectComparable, expectPattern) {
   Expect.equals(expectComparable, value is Comparable);
   Expect.equals(expectPattern, value is Pattern);
 }
 
 checkCast(value, expectComparable, expectPattern) {
   if (expectComparable) {
     Expect.identical(value, value as Comparable);
@@ skipping 12 matching lines @@
     [],
     4,
     4.2,
     'foo',
     new Object(),
     makeA(),
     makeB(),
     makeC(),
     makeD()
   ];
-  value(i) => things[inscrutable(i)];
+  value(i) => confuse(things[i]);
 
   check(value(0), false, false); // List
   check(value(1), true, false); // int
   check(value(2), true, false); // num
   check(value(3), true, true); // String
   check(value(4), false, false); // Object
   check(value(5), false, false); // A
   check(value(6), true, false); // B
   check(value(7), false, true); // C
   check(value(8), true, true); // D
 }
 
 main() {
+  nativeTesting();
   setup();
 
   checkAll(checkTest);
   checkAll(checkCast);
 }