Issue 27689. Fix incremental resolution with body modifiers changes.

pkg/analyzer/lib/src/generated/incremental_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.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 647 matching lines @@
                 oldParent is ConstructorDeclaration &&
                     newParent is ConstructorDeclaration ||
                 oldParent is MethodDeclaration &&
                     newParent is MethodDeclaration) {
               if (oldParents.length == i || newParents.length == i) {
                 return false;
               }
             } else if (oldParent is FunctionBody && newParent is FunctionBody) {
               if (oldParent is BlockFunctionBody &&
                   newParent is BlockFunctionBody) {
+                if (oldParent.isAsynchronous != newParent.isAsynchronous) {
+                  logger.log('Failure: body async mismatch.');
+                  return false;
+                }
+                if (oldParent.isGenerator != newParent.isGenerator) {
+                  logger.log('Failure: body generator mismatch.');
+                  return false;
+                }
                 oldNode = oldParent;
                 newNode = newParent;
                 found = true;
                 break;
               }
               logger.log('Failure: not a block function body.');
               return false;
             } else if (oldParent is FunctionExpression &&
                 newParent is FunctionExpression) {
               // skip
@@ skipping 625 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }