Align behavior of VM's ObjectMirror.setField with language semantics.

tests/lib/mirrors/set_field_with_final_test.dart

+// 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.
+
+library test.set_field_with_final;
+
+import 'dart:mirrors';
+import 'package:expect/expect.dart';
+
+class C {
+  final instanceField = 1;
+  get instanceGetter => 2;
+  static final staticFinal = 3;
+  static get staticGetter => 4;
+}
+
+final toplevelFinal = 5;
+get toplevelGetter => 6;
+
+main() {
+  InstanceMirror im = reflect(new C());
+  Expect.throws(() => im.setField(#instanceField, 7),
+                (e) => e is NoSuchMethodError);
+  Expect.throws(() => im.setField(#instanceGetter, 8),
+                (e) => e is NoSuchMethodError);
+
+  ClassMirror cm = im.type;
+  Expect.throws(() => cm.setField(#staticFinal, 9),
+                (e) => e is NoSuchMethodError);
+  Expect.throws(() => cm.setField(#staticGetter, 10),
+                (e) => e is NoSuchMethodError);
+
+  LibraryMirror lm = cm.owner;
+  Expect.throws(() => lm.setField(#toplevelFinal, 11),
+                (e) => e is NoSuchMethodError);
+  Expect.throws(() => lm.setField(#toplevelGetter, 12),
+                (e) => e is NoSuchMethodError);
+}