Add top-level driver and abstract plugin superclass

pkg/analyzer_plugin/lib/utilities/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/generated_protocol.dart';
+
+/**
+ * An object that manages the subscriptions for analysis results.
+ */
+class SubscriptionManager {
+  /**
+   * The current set of subscriptions.
+   */
+  Map<AnalysisService, List<String>> _subscriptions;
+
+  /**
+   * Initialize a newly created subscription manager to have no subscriptions.
+   */
+  SubscriptionManager();
+
+  /**
+   * 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);
+        }
+      });
+    }
+    return services;
+  }
+
+  /**
+   * Set the current set of subscriptions to those described by the given map of
+   * [subscriptions].
+   */
+  void setSubscriptions(Map<AnalysisService, List<String>> subscriptions) {
+    _subscriptions = subscriptions;
+  }
+}