Add support for asynchronous event notification to the observatory.

runtime/bin/vmservice/client/lib/service_html.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 service_html;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:html';
 
@@ skipping 77 matching lines @@
         socket.onClose.first.then((_) {
             _socketFuture = null;
           });
         completer.complete(socket);
       });
     socket.onError.first.then((_) {
         _socketFuture = null;
       });
   }
 
-  void _handleMessage(MessageEvent event) {
-    var map = JSON.decode(event.data);
+  void _handleMessage(MessageEvent message) {
+    var map = JSON.decode(message.data);
     int seq = map['seq'];
     var response = map['response'];
+    if (seq == null) {
+      // Messages without sequence numbers are asynchronous events
+      // from the vm.
+      postEventMessage(response);
+      return;
+    }
     var completer = _pendingRequests.remove(seq);
     if (completer == null) {
       Logger.root.severe('Received unexpected message: ${map}');
     } else {
       completer.complete(response);
     }
   }
 
   Future<String> getString(String id) {
     if (_socketFuture == null) {
@@ skipping 51 matching lines @@
     message['id'] = idString;
     message['method'] = 'observatoryQuery';
     message['query'] = '$path';
     _requestSerial++;
     var completer = new Completer();
     _pendingRequests[idString] = completer;
     window.parent.postMessage(JSON.encode(message), '*');
     return completer.future;
   }
 }