Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/native_null_closure_frog_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.
 
 // Test that exception unwrapping handle cases like ({foo:null}).foo().
 
-import "native_testing.dart";
+import "dart:_js_helper";
+
+import "package:expect/expect.dart";
 
 typedef void MyFunctionType();
 
 @Native("A")
 class A {
   setClosure(MyFunctionType f) native ;
   check(MyFunctionType f) native ;
   invoke() native ;
 }
 
 makeA() native ;
 
 void setup() native """
 function A() {}
 A.prototype.setClosure = function(f) { this.f = f; };
 A.prototype.check = function(f) { return this.f === f; };
 A.prototype.invoke = function() { return this.f(); };
 makeA = function(){return new A;};
-
-self.nativeConstructor(A);
 """;
 
 main() {
-  nativeTesting();
   setup();
   A a = makeA();
   a.setClosure(null);
   Expect.isTrue(a.check(null));
   bool caughtException = false;
   try {
     a.invoke();
-  } on NoSuchMethodError catch (e) {
+  } on JsNoSuchMethodError catch (e) {
     print(e);
     caughtException = true;
   }
   Expect.isTrue(caughtException);
 }