Use 'print' to send responses/notifications to the client.

pkg/analysis_server/lib/src/protocol.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 protocol;
 
 import 'dart:collection';
 import 'dart:convert';
 
 part 'generated_protocol.dart';
@@ skipping 451 matching lines @@
         json[Notification.EVENT],
         json[Notification.PARAMS]);
   }
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
     Map<String, Object> jsonObject = {};
+    jsonObject['time'] = new DateTime.now().millisecondsSinceEpoch;

[danrubel, 2015/01/23 14:16:53]

Good idea, but I already have a pending CL to capture the request time.
https://codereview.chromium.org/865383002/
Please remove this.

[scheglov, 2015/01/23 16:27:40]

Done.

     jsonObject[EVENT] = event;
     if (_params != null) {
       jsonObject[PARAMS] = _params;
     }
     return jsonObject;
   }
 }
 
 /**
  * Instances of the class [Request] represent a request that was received.
@@ skipping 340 matching lines @@
           requestId,
           error: new RequestError(RequestErrorCode.UNSUPPORTED_FEATURE, message));
 
   /**
    * Return a table representing the structure of the Json object that will be
    * sent to the client to represent this response.
    */
   Map<String, Object> toJson() {
     Map<String, Object> jsonObject = new HashMap<String, Object>();
     jsonObject[ID] = id;
+    jsonObject['time'] = new DateTime.now().millisecondsSinceEpoch;

[danrubel, 2015/01/23 14:16:53]

Please remove this as described above.

[scheglov, 2015/01/23 16:27:40]

Done.

     if (error != null) {
       jsonObject[ERROR] = error.toJson();
     }
     if (_result != null) {
       jsonObject[RESULT] = _result;
     }
     return jsonObject;
   }
 }
 
@@ skipping 34 matching lines @@
     hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
     hash = hash ^ (hash >> 11);
     return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
   }
 
   static int hash2(a, b) => finish(combine(combine(0, a), b));
 
   static int hash4(a, b, c, d) =>
       finish(combine(combine(combine(combine(0, a), b), c), d));
 }