Move definition of Feature next to definitions of WorldImpact and Use

pkg/compiler/lib/src/serialization/equivalence.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.
 
 /// Functions for asserting equivalence across serialization.
 
 library dart2js.serialization.equivalence;
 
 import '../closure.dart';
 import '../common/resolution.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../elements/visitor.dart';
 import '../js_backend/backend_serialization.dart'
     show NativeBehaviorSerialization;
 import '../native/native.dart' show NativeBehavior;
 import '../resolution/access_semantics.dart';
 import '../resolution/send_structure.dart';
 import '../resolution/tree_elements.dart';
 import '../tokens/token.dart';
 import '../tree/nodes.dart';
 import '../universe/selector.dart';
+import '../universe/feature.dart';
 import '../universe/use.dart';
 import '../util/util.dart';
 import 'resolved_ast_serialization.dart';
 
 /// Equality based equivalence function.
 bool equality(a, b) => a == b;
 
 /// Returns `true` if the elements in [a] and [b] are pair-wise equivalent
 /// according to [elementEquivalence].
 bool areListsEquivalent(List a, List b,
@@ skipping 1991 matching lines @@
 }
 
 bool areMetadataAnnotationsEquivalent(
     MetadataAnnotation metadata1, MetadataAnnotation metadata2) {
   if (metadata1 == metadata2) return true;
   if (metadata1 == null || metadata2 == null) return false;
   return areElementsEquivalent(
           metadata1.annotatedElement, metadata2.annotatedElement) &&
       areConstantsEquivalent(metadata1.constant, metadata2.constant);
 }