Use MemberEntity more in type_graph_nodes

pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart

 // Copyright (c) 2013, 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 type_graph_inferrer;
 
 import 'dart:collection' show Queue;
 
 import '../compiler.dart' show Compiler;
 import '../elements/elements.dart';
@@ skipping 118 matching lines @@
     TypeMask result = const TypeMask.nonNullEmpty();
     Iterable<MemberEntity> elements =
         inferrer.closedWorld.locateMembers(selector, mask);
     for (MemberElement element in elements) {
       TypeMask type = inferrer.typeOfMemberWithSelector(element, selector).type;
       result = result.union(type, inferrer.closedWorld);
     }
     return result;
   }
 
-  Iterable<Element> getCallersOf(MemberElement element) {
+  Iterable<MemberEntity> getCallersOf(MemberElement element) {
     if (compiler.disableTypeInference) {
       throw new UnsupportedError(
           "Cannot query the type inferrer when type inference is disabled.");
     }
     return inferrer.getCallersOf(element);
   }
 
   bool isMemberCalledOnce(MemberElement element) {
     if (compiler.disableTypeInference) return false;
     MemberTypeInformation info =
         inferrer.types.getInferredTypeOfMember(element);
     return info.isCalledOnce();
   }
 
   void clear() {
     inferrer.clear();
   }
 }