Make more use of generated code in analysis server.

pkg/analysis_server/test/analysis_server_test.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 test.analysis_server;
 
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_server.dart';
@@ skipping 104 matching lines @@
     server = new AnalysisServer(channel, PhysicalResourceProvider.INSTANCE,
         new MockPackageMapProvider(), null, new MockSdk(),
         rethrowExceptions: rethrowExceptions);
   }
 }
 
 class EchoHandler implements RequestHandler {
   @override
   Response handleRequest(Request request) {
     if (request.method == 'echo') {
-      var response = new Response(request.id);
-      response.setResult('echo', true);
-      return response;
+      return new Response(request.id, result: {'echo': true});
     }
     return null;
   }
 }