more progress implementing analysis server code completion

pkg/analysis_server/lib/src/collections.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 collections;
 
 /**
  * Returns the concatentation of the input iterables.
  *
  * The returned iterable is a lazily-evaluated view on the input iterables.
  */
 Iterable concat(Iterable<Iterable> iterables) => iterables.expand((x) => x);
 
 
 /**
  * Returns the concatentation of the input iterables as a [List].
  */
 List concatToList(Iterable<Iterable> iterables) => concat(iterables).toList();
-
-
-/**
- * Instances of the class [HasToJson] implement [toJson] method that returns
- * a JSON presentation.
- */
-abstract class HasToJson {
-  /**
-   * Returns a JSON presentation of the object.
-   */
-  Map<String, Object> toJson();
-}