Make .enclosingClass always return the declaration

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

 // Copyright (c) 2017, 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.
 
 import '../common.dart';
 import '../common/names.dart';
 import '../compiler.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
 import '../core_types.dart';
@@ skipping 816 matching lines @@
         node,
         caller,
         callee,
         selector,
         mask,
         arguments,
         inLoop);
     // If this class has a 'call' method then we have essentially created a
     // closure here. Register it as such so that it is traced.
     if (selector != null && selector.isCall && callee.isConstructor) {
-      ClassElement cls = callee.enclosingClass.declaration;
+      ClassElement cls = callee.enclosingClass;
       if (cls.callType != null) {
         types.allocatedClosures.add(info);
       }
     }
     info.addToGraph(this);
     allocatedCalls.add(info);
     updateSideEffects(sideEffects, selector, callee);
     return info;
   }
 
@@ skipping 194 matching lines @@
   /**
    * Records that the captured variable [local] is read.
    */
   void recordCapturedLocalRead(Local local) {}
 
   /**
    * Records that the variable [local] is being updated.
    */
   void recordLocalUpdate(Local local, TypeInformation type) {}
 }