Use Set<ClassEntity> instead of Set<MixinApplicationElement>

pkg/compiler/lib/src/world.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 dart2js.world;
 
 import 'closure.dart' show ClosureClassElement, SynthesizedCallMethodElementX;
 import 'common/backend_api.dart' show BackendClasses;
 import 'common.dart';
 import 'constants/constant_system.dart';
@@ skipping 823 matching lines @@
     assert(isClosed);
     if (_liveMixinUses == null) {
       _liveMixinUses = new Map<ClassElement, List<MixinApplicationElement>>();
       for (ClassElement mixin in _mixinUses.keys) {
         List<MixinApplicationElement> uses = <MixinApplicationElement>[];
 
         void addLiveUse(MixinApplicationElement mixinApplication) {
           if (isInstantiated(mixinApplication)) {
             uses.add(mixinApplication);
           } else if (mixinApplication.isNamedMixinApplication) {
-            Set<MixinApplicationElement> next = _mixinUses[mixinApplication];
+            Set<ClassEntity> next = _mixinUses[mixinApplication];
             if (next != null) {
               next.forEach(addLiveUse);
             }
           }
         }
 
         _mixinUses[mixin].forEach(addLiveUse);
         if (uses.isNotEmpty) {
           _liveMixinUses[mixin] = uses;
         }
@@ skipping 337 matching lines @@
       return getMightBePassedToApply(element.expression);
     }
     return functionsThatMightBePassedToApply.contains(element);
   }
 
   @override
   bool getCurrentlyKnownMightBePassedToApply(Element element) {
     return getMightBePassedToApply(element);
   }
 }