Alternative fix for the js-interop crash.

tests/html/js_typed_interop_side_cast_exp_test.dart

Index: tests/html/js_typed_interop_side_cast_exp_test.dart
diff --git a/tests/html/js_typed_interop_side_cast_exp_test.dart b/tests/html/js_typed_interop_side_cast_exp_test.dart
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index 0000000000000000000000000000000000000000..6fd929a6fc9c1265a9fcbe328c4f8fb1e92382d1
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+++ b/tests/html/js_typed_interop_side_cast_exp_test.dart
@@ -0,0 +1,53 @@
+// Copyright (c) 2015, 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.
+//
+// SharedOptions=--experimental-trust-js-interop-type-annotations
+
+// Similar test to js_typed_interop_side_cast, but because we are using the
+// --experimental-trust-js-interop-type-annotations flag, we test a slighly
+// different behavior.
+library js_typed_interop_side_cast_exp_test;
+
+import 'dart:html';
+import 'dart:js' as js;
+
+import 'package:js/js.dart';
+import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
+
+@JS() @anonymous
+class A {
+  external int get x;
+  external factory A({int x});
+}
+
+@JS() @anonymous
+class B {
+  external int get x;
+  external factory B({int x});
+}
+
+@JS() @anonymous
+class C {
+  external int get x;
+  external factory C({int x});
+}
+
+main() {
+  useHtmlConfiguration();
+
+  test('side-casts work for reachable types', () {
+    new C(x: 3); // make C reachable
+    var a = new A(x: 3);
+    expect(a is C, isTrue);
+    C c = a;
+    expect(c.x, equals(3));
+  });
+
+  // Note: this test would fail without the experimental flag.
+  test('side-casts do not work for unreachable types', () {
+    var a = new A(x: 3);
+    expect(a is B, isFalse);
+  });
+}