Use HasToJson when set Reponse/Notification parameters.

pkg/analysis_server/lib/src/computer/computer_occurrences.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 computer.occurrences;
 
 import 'dart:collection';
 
+import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/computer/element.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
 
 
 /**
  * A computer for elements occurrences in a Dart [CompilationUnit].
  */
 class DartUnitOccurrencesComputer {
   final CompilationUnit _unit;
 
   final Map<engine.Element, List<int>> _elementsOffsets =
       new HashMap<engine.Element, List<int>>();
 
   DartUnitOccurrencesComputer(this._unit);
 
   /**
    * Returns the computed occurrences, not `null`.
    */
-  List<Map<String, Object>> compute() {
+  List<Occurrences> compute() {
     _unit.accept(new _DartUnitOccurrencesComputerVisitor(this));
     List<Occurrences> occurrences = <Occurrences>[];
     _elementsOffsets.forEach((engineElement, offsets) {
       Element serverElement = new Element.fromEngine(engineElement);
       int length = engineElement.displayName.length;
       occurrences.add(new Occurrences(serverElement, offsets, length));
     });
-    return occurrences.map((occurrences) => occurrences.toJson()).toList();
+    return occurrences;
   }
 
   void _addOccurrence(engine.Element element, int offset) {
     List<int> offsets = _elementsOffsets[element];
     if (offsets == null) {
       offsets = <int>[];
       _elementsOffsets[element] = offsets;
     }
     offsets.add(offset);
   }
 }
 
 
-class Occurrences {
+class Occurrences implements HasToJson {
   final Element element;
   final List<int> offsets;
   final int length;
 
   Occurrences(this.element, this.offsets, this.length);
 
   factory Occurrences.fromJson(Map<String, Object> map) {
     Element element = new Element.fromJson(map[ELEMENT]);
     List<int> offsets = map[OFFSETS];
     int length = map[LENGTH];
@@ skipping 20 matching lines @@
 
   @override
   visitSimpleIdentifier(SimpleIdentifier node) {
     engine.Element element = node.bestElement;
     if (element != null) {
       computer._addOccurrence(element, node.offset);
     }
     return super.visitSimpleIdentifier(node);
   }
 }