Add utility method to SubscriptionManager

pkg/analyzer_plugin/lib/utilities/subscriptions/subscription_manager.dart

 // Copyright (c) 2017, 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.
 
 import 'package:analyzer_plugin/protocol/protocol_generated.dart';
 
 /**
  * An object that manages the subscriptions for analysis results.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 class SubscriptionManager {
   /**
    * The current set of subscriptions.
    */
   Map<AnalysisService, List<String>> _subscriptions;
 
   /**
    * Initialize a newly created subscription manager to have no subscriptions.
    */
   SubscriptionManager();
 
   /**
+   * Return `true` if the file with the given [filePath] has a subscription for
+   * the given [service].
+   */
+  bool hasSubscriptionForFile(String filePath, AnalysisService service) {
+    if (_subscriptions == null) {
+      return false;
+    }
+    List<String> files = _subscriptions[service];
+    return files != null && files.contains(filePath);
+  }
+
+  /**
    * Return a list of the services for which the file with the given [filePath]
    * has been subscribed.
    */
   List<AnalysisService> servicesForFile(String filePath) {
     List<AnalysisService> services = <AnalysisService>[];
     if (_subscriptions != null) {
       _subscriptions.forEach((AnalysisService service, List<String> files) {
         if (files.contains(filePath)) {
           services.add(service);
         }
@@ skipping 35 matching lines @@
                 .putIfAbsent(path, () => <AnalysisService>[])
                 .add(service);
           }
         }
       });
     }
     _subscriptions = subscriptions;
     return newSubscriptions;
   }
 }