pkg/compiler: fix imports

pkg/compiler/lib/src/serialization/serialization.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;
 
 import '../common.dart';
 import '../common/resolution.dart';
 import '../constants/expressions.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../library_loader.dart' show LibraryProvider;
 import '../util/enumset.dart';
-
 import 'constant_serialization.dart';
 import 'element_serialization.dart';
 import 'json_serializer.dart';
 import 'keys.dart';
 import 'type_serialization.dart';
 import 'values.dart';
 
 export 'task.dart' show LibraryDeserializer;
 
 /// An object that supports the encoding an [ObjectValue] for serialization.
@@ skipping 1105 matching lines @@
 
   /// Returns the value used to store [key] as a property in the encoding an
   /// [ObjectValue].
   ///
   /// Different encodings have different restrictions and capabilities as how
   /// to store a [Key] value. For instance: A JSON encoding needs to convert
   /// [Key] to a [String] to store it in a JSON object; a Dart encoding can
   /// choose to store a [Key] as an [int] or as the [Key] itself.
   getObjectPropertyValue(Key key);
 }