Don't hide interceptors in mirrors.

tests/lib/mirrors/superclass2_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.superclass;
+
+import 'dart:mirrors';
+import 'package:expect/expect.dart';
+
+checkSuperclassChain(ClassMirror cm) {
+  ClassMirror last;
+  do {
+    last = cm;
+    cm = cm.superclass;
+  } while (cm != null);
+  Expect.equals(reflectClass(Object), last);
+}
+
+main() {
+  checkSuperclassChain(reflect(null).type);
+  checkSuperclassChain(reflect([]).type);
+  checkSuperclassChain(reflect(<int>[]).type);
+  checkSuperclassChain(reflect(0).type);
+  checkSuperclassChain(reflect(1.5).type);
+  checkSuperclassChain(reflect("str").type);
+  checkSuperclassChain(reflect(true).type);
+  checkSuperclassChain(reflect(false).type);
+}