Discard pending notifications on the same source change.

pkg/analysis_server/lib/src/operation/operation.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 operation;
 
 import 'package:analysis_server/src/analysis_server.dart';
+import 'package:analyzer/src/generated/source.dart';
 
 
 /**
  * The class [ServerOperation] defines the behavior of objects used to perform
  * operations on a [AnalysisServer].
  */
 abstract class ServerOperation {
   /**
    * Returns the priority of this operation.
    */
@@ skipping 33 matching lines @@
       const ServerOperationPriority._(5, "ANALYSIS");
 
   final int ordinal;
   final String name;
 
   const ServerOperationPriority._(this.ordinal, this.name);
 
   @override
   String toString() => name;
 }
+
+
+/**
+ * [SourceSensitiveOperation] can decide if the operation should be discarded
+ * before a change is applied to a [Source].
+ */
+abstract class SourceSensitiveOperation extends ServerOperation {
+  /**
+   * The given [source] is about to be changed.
+   * Check if this [SourceSensitiveOperation] should be discarded.
+   */
+  bool shouldBeDiscardedOnSourceChange(Source source);
+}