Addresses a ClassCastException seen in the editor from MemberBuilder

tests/language/src/DefaultFactoryLibraryTest.dart

Index: tests/language/src/DefaultFactoryLibraryTest.dart
diff --git a/tests/language/src/DefaultFactoryLibraryTest.dart b/tests/language/src/DefaultFactoryLibraryTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2b84c5b66f7a1828ed6102682b96e0e74dc78e81
--- /dev/null
+++ b/tests/language/src/DefaultFactoryLibraryTest.dart
@@ -0,0 +1,25 @@
+// Copyright (c) 2011, 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.
+
+// Dart test program for testing default factories defined across libraries
+
+#library("test");
+#import("DefaultFactoryLibrary.dart", prefix:"lib");
+
+class B implements lib.A {
+  int methodA() { return 1; }
+  int methodB() { return 2; }
+}
+
+class C {
+  // References an interface in another library
+  factory lib.A () { return new B(); }
+}
+
+main() {
+  var val = new lib.A();
+  Expect.equals(true, (val is B));
+  Expect.equals(1, val.methodA());
+  Expect.equals(2, val.methodB());
+}