Fix some issues in element serialization.

pkg/compiler/lib/src/serialization/keys.dart

 // Copyright (c) 2015, 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 dart2js.serialization.keys;
 
 /// Keys used for serialization.
 class Key {
   static const Key ALIAS = const Key('alias');
   static const Key ARGUMENTS = const Key('arguments');
+  static const Key ASYNC_MARKER = const Key('asyncMarker');
   static const Key BOUND = const Key('bound');
   static const Key CACHED_TYPE = const Key('cachedType');
   static const Key CALL_STRUCTURE = const Key('callStructure');
   static const Key CALL_TYPE = const Key('callType');
   static const Key CANONICAL_URI = const Key('canonicalUri');
   static const Key CLASS = const Key('class');
   static const Key COMPILATION_UNIT = const Key('compilation-unit');
   static const Key COMPILATION_UNITS = const Key('compilation-units');
   static const Key CONDITION = const Key('condition');
   static const Key CONSTANT = const Key('constant');
@@ skipping 94 matching lines @@
   static const Key URI = const Key('uri');
   static const Key VALUE = const Key('value');
   static const Key VALUES = const Key('values');
 
   final String name;
 
   const Key(this.name);
 
   String toString() => name;
 }