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

pkg/analyzer/lib/src/dart/element/type.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.type;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 1363 matching lines @@
   @override
   bool get isDartAsyncFuture {
     ClassElement element = this.element;
     if (element == null) {
       return false;
     }
     return element.name == "Future" && element.library.isDartAsync;
   }
 
   @override
+  bool get isDartAsyncFutureOr {
+    ClassElement element = this.element;
+    if (element == null) {
+      return false;
+    }
+    return element.name == "FutureOr" && element.library.isDartAsync;
+  }
+
+  @override
   bool get isDartCoreFunction {
     ClassElement element = this.element;
     if (element == null) {
       return false;
     }
     return element.name == "Function" && element.library.isDartCore;
   }
 
   @override
   bool get isDartCoreNull {
@@ skipping 976 matching lines @@
   @override
   Element get element => _element;
 
   @override
   bool get isBottom => false;
 
   @override
   bool get isDartAsyncFuture => false;
 
   @override
+  bool get isDartAsyncFutureOr => false;
+
+  @override
   bool get isDartCoreFunction => false;
 
   @override
   bool get isDartCoreNull => false;
 
   @override
   bool get isDynamic => false;
 
   @override
   bool get isObject => false;
@@ skipping 401 matching lines @@
 
   @override
   TypeImpl pruned(List<FunctionTypeAliasElement> prune) => this;
 
   @override
   VoidTypeImpl substitute2(
           List<DartType> argumentTypes, List<DartType> parameterTypes,
           [List<FunctionTypeAliasElement> prune]) =>
       this;
 }