add ContextsChangedEvent

pkg/analyzer/lib/src/generated/engine.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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine;
 
 import 'dart:collection';
@@ skipping 266 matching lines @@
  * up-to-date. For such clients there is a mechanism that allows them to incrementally perform
  * needed analysis and get notified of the consequent changes to the analysis results. This
  * mechanism is realized by the method [performAnalysisTask].
  *
  * Analysis engine allows for having more than one context. This can be used, for example, to
  * perform one analysis based on the state of files on disk and a separate analysis based on the
  * state of those files in open editors. It can also be used to perform an analysis based on a
  * proposed future state, such as the state after a refactoring.
  */
 abstract class AnalysisContext {
+
+  /**
+   * An empty list of contexts.
+   */
+  static const List<AnalysisContext> EMPTY_LIST = const <AnalysisContext>[];
+
   /**
    * Add the given listener to the list of objects that are to be notified when various analysis
    * results are produced in this context.
    *
    * @param listener the listener to be added
    */
   void addListener(AnalysisListener listener);
 
   /**
    * Apply the given delta to change the level of analysis that will be performed for the sources
@@ skipping 13225 matching lines @@
     _index++;
     if (_index >= _manager._workQueues[_queueIndex].length) {
       _index = 0;
       _queueIndex++;
       while (_queueIndex < _manager._workQueues.length && _manager._workQueues[_queueIndex].isEmpty) {
         _queueIndex++;
       }
     }
   }
 }