Test for JS objects spoofing Dart objects

tests/compiler/dart2js_native/fake_thing_test.dart

Index: tests/compiler/dart2js_native/fake_thing_test.dart
diff --git a/tests/compiler/dart2js_native/fake_thing_test.dart b/tests/compiler/dart2js_native/fake_thing_test.dart
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+++ b/tests/compiler/dart2js_native/fake_thing_test.dart
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+// 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 "package:expect/expect.dart";
+
+// Test that native objects cannot accidentally or maliciously be mistaken for
+// Dart objects.
+
+class Thing {
+}
+
+make1() native;
+make2() native;
+
+void setup() native r"""
+function A() {}
+A.prototype.$isThing = true;
+make1 = function(){return new A;};
+make2 = function(){return {$isThing: true}};
+""";
+
+var inscrutable;
+main() {
+  setup();
+  inscrutable = (x) => x;
+
+  var a = new Thing();
+  var b = make1();
+  var c = make2();
+  Expect.isTrue(inscrutable(a) is Thing);
+  Expect.isFalse(inscrutable(b) is Thing);
+  Expect.isFalse(inscrutable(c) is Thing);
+}