fix #28008, fix #28009 implement FutureOr<T>

pkg/analyzer/lib/src/dart/element/element.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.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 7868 matching lines @@
   void set propagatedType(DartType propagatedType) {
     _assertNotResynthesized(_unlinkedVariable);
     _propagatedType = propagatedType;
   }
 }
 
 /**
  * The context in which elements are resynthesized.
  */
 abstract class ResynthesizerContext {
+  bool get isStrongMode;
+
   /**
    * Build [ElementAnnotationImpl] for the given [UnlinkedExpr].
    */
   ElementAnnotationImpl buildAnnotation(ElementImpl context, UnlinkedExpr uc);
 
   /**
    * Build [Expression] for the given [UnlinkedExpr].
    */
   Expression buildExpression(ElementImpl context, UnlinkedExpr uc);
 
@@ skipping 717 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }