allow --dart-sdk with --persisent_worker

pkg/analyzer_cli/lib/src/options.dart

 // Copyright (c) 2015, 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_cli.src.options;
 
 import 'dart:io';
 
 import 'package:analyzer_cli/src/driver.dart';
 import 'package:args/args.dart';
@@ skipping 447 matching lines @@
 
     try {
       // TODO(scheglov) https://code.google.com/p/dart/issues/detail?id=11061
       args =
           args.map((String arg) => arg == '-batch' ? '--batch' : arg).toList();
       Map<String, String> definedVariables = <String, String>{};
       var results = parser.parse(args, definedVariables);
 
       // Persistent worker.
       if (args.contains('--persistent_worker')) {
-        if (args.length != 2 || !args.contains('--build-mode')) {
+        bool validArgs;
+        if (!args.contains('--build-mode')) {
+          validArgs = false;
+        } else if (args.length == 2) {
+          validArgs = true;
+        } else if (args.length == 4 && args.contains('--dart-sdk')) {
+          validArgs = true;
+        } else {
+          validArgs = false;
+        }
+        if (!validArgs) {
           printAndFail('The --persistent_worker flag should be used with and '
-              'only with the --build-mode flag.');
+              'only with the --build-mode flag, and possibly the --dart-sdk '
+              'option. Got: $args');
           return null; // Only reachable in testing.
         }
         return new CommandLineOptions._fromArgs(results, definedVariables);
       }
 
       // Help requests.
       if (results['help']) {
         _showUsage(parser);
         exitHandler(0);
         return null; // Only reachable in testing.
@@ skipping 178 matching lines @@
 
   int _getNextFlagIndex(args, i) {
     for (; i < args.length; ++i) {
       if (args[i].startsWith('--')) {
         return i;
       }
     }
     return i;
   }
 }