Make analyzer more strong mode compliant

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 6505 matching lines @@
    * The object used to compute the type associated with the current node.
    */
   StaticTypeAnalyzer typeAnalyzer;
 
   /**
    * The type system in use during resolution.
    */
   TypeSystem typeSystem;
 
   /**
-   * The class element representing the class containing the current node,
-   * or `null` if the current node is not contained in a class.
-   */
-  @override
-  ClassElement enclosingClass = null;
-
-  /**
    * The class declaration representing the class containing the current node, or `null` if
    * the current node is not contained in a class.
    */
   ClassDeclaration _enclosingClassDeclaration = null;
 
   /**
    * The function type alias representing the function type containing the current node, or
    * `null` if the current node is not contained in a function type alias.
    */
   FunctionTypeAlias _enclosingFunctionTypeAlias = null;
@@ skipping 5413 matching lines @@
     nonFields.add(node);
     return null;
   }
 
   @override
   Object visitNode(AstNode node) => node.accept(TypeResolverVisitor_this);
 
   @override
   Object visitWithClause(WithClause node) => null;
 }