Support for Null as bottom in dart2js

tests/language/null_is_bottom_type_test.dart

Index: tests/language/null_is_bottom_type_test.dart
diff --git a/tests/language/null_is_bottom_type_test.dart b/tests/language/null_is_bottom_type_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b12137efebd70f9b90f16bafc3f7ddaae6853824
--- /dev/null
+++ b/tests/language/null_is_bottom_type_test.dart
@@ -0,0 +1,60 @@
+// Copyright (c) 2016, 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 Null is a subtype of any other type.
+
+import 'package:expect/expect.dart';
+
+class A {}
+typedef A ReturnA();
+typedef TakeA(A a);
+typedef Null ReturnNull();
+typedef TakeNull(Null n);
+
+testA(A a) {}
+testListA(List<A> list) {}
+testNull(Null n) {}
+testListNull(List<Null> list) {}
+testReturnA(ReturnA f) {}
+testReturnNull(ReturnNull f) {}
+testTakeA(TakeA f) {}
+testTakeNull(TakeNull f) {}
+
+Null returnNull() => null;
+takeNull(Null n) {}
+A returnA() => null;
+takeA(A a) {}
+
+main() {
+  if (false) test(); // Perform static checks only.
+}
+
+test() {
+  Null n;
+  List<Null> listNull;
+  A a = new A();
+  List<A> listA;
+
+  testA(n);                                                          /// 01: ok
+  testA(a);                                                          /// 02: ok
+  testListA(listNull);                                               /// 03: ok
+  testListA(listA);                                                  /// 04: ok
+
+  testNull(n);                                                       /// 05: ok
+  testNull(a);                                                       /// 06: ok
+  testListNull(listNull);                                            /// 07: ok
+  testListNull(listA);                                               /// 08: ok
+
+  testReturnA(returnA);                                              /// 09: ok
+  testReturnA(returnNull);                                           /// 10: ok
+
+  testReturnNull(returnA);                                           /// 11: ok
+  testReturnNull(returnNull);                                        /// 12: ok
+
+  testTakeA(takeA);                                                  /// 13: ok
+  testTakeA(takeNull);                                               /// 14: ok
+
+  testTakeNull(takeA);                                               /// 15: ok
+  testTakeNull(takeNull);                                            /// 16: ok
+}