Prepare for decoupling analyzer ASTs from element model.

pkg/analysis_server/lib/src/services/index/index_unit.dart

 // Copyright (c) 2016, 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 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/resolution_accessors.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/format.dart';
 import 'package:analyzer/src/summary/idl.dart';
 
 /**
@@ skipping 466 matching lines @@
 
   @override
   visitBinaryExpression(BinaryExpression node) {
     recordOperatorReference(node.operator, node.bestElement);
     super.visitBinaryExpression(node);
   }
 
   @override
   visitClassDeclaration(ClassDeclaration node) {
     if (node.extendsClause == null) {
-      ClassElement objectElement = node.element.supertype?.element;
+      ClassElement objectElement =
+          elementForClassDeclaration(node).supertype?.element;
       recordRelationOffset(objectElement, IndexRelationKind.IS_EXTENDED_BY,
           node.name.offset, 0, true);
     }
     recordIsAncestorOf(node.element);
     super.visitClassDeclaration(node);
   }
 
   @override
   visitClassTypeAlias(ClassTypeAlias node) {
     recordIsAncestorOf(node.element);
@@ skipping 396 matching lines @@
         usedNameOffsets: nameRelations.map((r) => r.offset).toList(),
         usedNameIsQualifiedFlags:
             nameRelations.map((r) => r.isQualified).toList());
   }
 
   void defineName(String name, IndexNameKind kind, int offset) {
     _StringInfo nameInfo = pkg._getStringInfo(name);
     definedNames.add(new _DefinedNameInfo(nameInfo, kind, offset));
   }
 }