pkg/compiler: fix imports

pkg/compiler/lib/src/js_backend/backend_serialization.dart

 // Copyright (c) 2016, 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 js_backend.serialization;
 
 import '../common/backend_api.dart' show BackendSerialization;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../js/js.dart' as js;
 import '../native/native.dart';
+import '../serialization/keys.dart';
 import '../serialization/serialization.dart'
     show DeserializerPlugin, ObjectDecoder, ObjectEncoder, SerializerPlugin;
-import '../serialization/keys.dart';
 import '../universe/side_effects.dart';
 import 'js_backend.dart';
 
 const String _BACKEND_DATA_TAG = 'jsBackendData';
 const Key DART_TYPES_RETURNED = const Key('dartTypesReturned');
 const Key THIS_TYPES_RETURNED = const Key('thisTypesReturned');
 const Key SPECIAL_TYPES_RETURNED = const Key('specialTypesReturned');
 const Key DART_TYPES_INSTANTIATED = const Key('dartTypesInstantiated');
 const Key THIS_TYPES_INSTANTIATED = const Key('thisTypesInstantiated');
 const Key SPECIAL_TYPES_INSTANTIATED = const Key('specialTypesInstantiated');
@@ skipping 224 matching lines @@
       behavior.codeTemplate = js.js.parseForeignJS(behavior.codeTemplateText);
     }
 
     behavior.throwBehavior =
         decoder.getEnum(THROW_BEHAVIOR, NativeThrowBehavior.values);
     behavior.isAllocation = decoder.getBool(IS_ALLOCATION);
     behavior.useGvn = decoder.getBool(USE_GVN);
     return behavior;
   }
 }