Change analysis server protocol to omit empty lists when optional.

pkg/analysis_server/lib/src/search/search_result.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 search.search_result;
 
 import 'package:analysis_server/src/protocol2.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
 
 
 SearchResult searchResultFromMatch(SearchMatch match) {
   SearchResultKind kind = new SearchResultKind.fromEngine(match.kind);
   Location location =
       new Location.fromOffset(
           match.element,
           match.sourceRange.offset,
           match.sourceRange.length);
   List<Element> path = _computePath(match.element);
-  return new SearchResult(location, kind, !match.isResolved, path);
+  return new SearchResult(location, kind, !match.isResolved, path: path);
 }
 
 List<Element> _computePath(engine.Element element) {
   List<Element> path = <Element>[];
   while (element != null) {
     path.add(new Element.fromEngine(element));
     element = element.enclosingElement;
   }
   return path;
 }