Re-triage mirror test failures on the analyzer.

tests/lib/mirrors/mixin_members_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 mixin_members_test;
 
 import "dart:mirrors";
 
 import "package:expect/expect.dart";
 
 import 'stringify.dart';
 
-class Fooer {
+abstract class Fooer {
   foo1();
 }
 
 class S implements Fooer {
   foo1() {}
   foo2() {}
 }
 
 class M1 {
   bar1() {}
@@ skipping 23 matching lines @@
          // TODO(ahe): Shouldn't have to sort.
          sort(sM1.members.keys), '(S with M1).members');
   expect('[s(M1)]', simpleNames(sM1.superinterfaces),
          '(S with M1).superinterfaces');
   expect('[s(foo1), s(foo2)]',
          // TODO(ahe): Shouldn't have to sort.
          sort(s.members.keys), 's.members');
   expect('[s(Fooer)]', simpleNames(s.superinterfaces), 's.superinterfaces');
   Expect.equals(s, reflectClass(S));
 }