Revert "Add native_testing library to mock @Native classes"

tests/compiler/dart2js_native/native_mixin_multiple3_test.dart

Index: tests/compiler/dart2js_native/native_mixin_multiple3_test.dart
diff --git a/tests/compiler/dart2js_native/native_mixin_multiple3_test.dart b/tests/compiler/dart2js_native/native_mixin_multiple3_test.dart
index ccbdd0cce1cb77fdb055ecca63374f441233a249..3b8875ce5fb7f2d594c9180bb6e095a246cf7d44 100644
--- a/tests/compiler/dart2js_native/native_mixin_multiple3_test.dart
+++ b/tests/compiler/dart2js_native/native_mixin_multiple3_test.dart
@@ -2,7 +2,8 @@
 // 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 native classes and plain classes can access methods defined only by
 // the same mixin.
@@ -45,10 +46,6 @@ function C() {}
 makeA = function(){return new A;};
 makeB = function(){return new B;};
 makeC = function(){return new C;};
-
-self.nativeConstructor(A);
-self.nativeConstructor(B);
-self.nativeConstructor(C);
 """;
 
 var g;
@@ -65,7 +62,6 @@ callFoo(x) {
 makeAll() => [makeA(), makeB(), makeC(), new D(), new E()];
 
 main() {
-  nativeTesting();
   setup();
   /*
   var a = makeA();