Specialize the return type of a factory constructor to be the enclosing type.

tests/language/factory_return_type_checked_test.dart

Index: tests/language/factory_return_type_checked_test.dart
===================================================================
--- tests/language/factory_return_type_checked_test.dart	(revision 0)
+++ tests/language/factory_return_type_checked_test.dart	(revision 0)
@@ -0,0 +1,23 @@
+// 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";
+
+class A {
+  factory A() => 42;
+}
+
+main() {
+  bool isCheckedMode = false;
+  try {
+    String a = 42;
+  } catch (e) {
+    isCheckedMode = true;
+  }
+  if (isCheckedMode) {
+    Expect.throws(() => new A(), (e) => e is TypeError);
+  } else {
+    Expect.equals(42, new A());
+  }
+}