Use ExitDetector.exists(node).

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 engine.resolver;
 
 import "dart:math" as math;
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/utilities_collection.dart';
@@ skipping 580 matching lines @@
     if (returnTypeType == null || returnTypeType.isVoid) {
       return false;
     }
     // For async, give no hint if Future<Null> is assignable to the return
     // type.
     if (body.isAsynchronous && _futureNullType.isAssignableTo(returnTypeType)) {
       return false;
     }
     // Check the block for a return statement, if not, create the hint
     BlockFunctionBody blockFunctionBody = body as BlockFunctionBody;
-    if (!blockFunctionBody.accept(new ExitDetector())) {
+    if (!ExitDetector.exits(blockFunctionBody)) {
       _errorReporter.reportErrorForNode(
           HintCode.MISSING_RETURN,
           returnType,
           [returnTypeType.displayName]);
       return true;
     }
     return false;
   }
 
   /**
@@ skipping 15082 matching lines @@
    * library.
    */
   final HashSet<String> members = new HashSet<String>();
 
   /**
    * Names of resolved or unresolved class members that are read in the
    * library.
    */
   final HashSet<String> readMembers = new HashSet<String>();
 }