Turn compile time errors related to missing getters and setters into invocation

tests/language/assign_top_method_test.dart

Index: tests/language/assign_top_method_test.dart
===================================================================
--- tests/language/assign_top_method_test.dart	(revision 16382)
+++ tests/language/assign_top_method_test.dart	(working copy)
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 
@@ -6,5 +6,6 @@
 
 main() {
   // Illegal, can't change a top level method
-  method = () { return 1; };
+  Expect.throws(() { method = () { return 1; }; },
+                (e) => e is NoSuchMethodError);
 }