Specify when 'sortMembers' will return an error.

editor/tools/plugins/com.google.dart.server/src/com/google/dart/server/AnalysisServer.java

 /*
  * Copyright (c) 2014, the Dart project authors.
  *
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
  *
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Unless required by applicable law or agreed to in writing, software distributed under the License
  * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
@@ skipping 234 matching lines @@
    *         omitted if the refactoring does not require any options or if the values of those
    *         options are not known.
    */
   public void edit_getRefactoring(String kind, String file, int offset, int length, boolean validateOnly, RefactoringOptions options, GetRefactoringConsumer consumer);
 
   /**
    * {@code edit.sortMembers}
    *
    * Sort all of the directives, unit and class members of the given Dart file.
    *
+   * It is an error if the file does not exist or has scan or parse errors.
+   *
    * @param file The Dart file to sort.
    */
   public void edit_sortMembers(String file, SortMembersConsumer consumer);
 
   /**
    * {@code execution.createContext}
    *
    * Create an execution context for the executable file with the given path. The context that is
    * created will persist until execution.deleteContext is used to delete it. Clients, therefore, are
    * responsible for managing the lifetime of execution contexts.
@@ skipping 140 matching lines @@
    * the response to this request has been sent.
    */
   public void server_shutdown();
 
   /**
    * Start the analysis server.
    */
   public void start() throws Exception;
 
 }