Use entities in Selector methods

pkg/compiler/lib/src/elements/elements.dart

 // Copyright (c) 2012, 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 elements;
 
 import 'package:front_end/src/fasta/parser/async_modifier.dart'
     show AsyncModifier;
 
 import '../common.dart';
@@ skipping 1658 matching lines @@
   void addBackendMember(Element element);
   void reverseBackendMembers();
 
   Element lookupMember(String memberName);
 
   /// Looks up a class instance member declared or inherited in this class
   /// using [memberName] to match the (private) name and getter/setter property.
   ///
   /// This method recursively visits superclasses until the member is found or
   /// [stopAt] is reached.
-  Element lookupByName(Name memberName, {ClassElement stopAt});
-  Element lookupSuperByName(Name memberName);
+  MemberElement lookupByName(Name memberName, {ClassElement stopAt});
+  MemberElement lookupSuperByName(Name memberName);
 
   Element lookupLocalMember(String memberName);
   Element lookupBackendMember(String memberName);
   Element lookupSuperMember(String memberName);
 
   Element lookupSuperMemberInLibrary(String memberName, LibraryElement library);
 
   // TODO(johnniwinther): Clean up semantics. Can the default constructor take
   // optional arguments? Must it be resolved?
   ConstructorElement lookupDefaultConstructor();
@@ skipping 342 matching lines @@
   /// by a field.
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }