Add VMService GC events

runtime/bin/vmservice/server.dart

 // Copyright (c) 2013, 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.
 
 part of vmservice_io;
 
 class WebSocketClient extends Client {
   static const int PARSE_ERROR_CODE = 4000;
   static const int BINARY_MESSAGE_ERROR_CODE = 4001;
   static const int NOT_MAP_ERROR_CODE = 4002;
   final WebSocket socket;
 
   WebSocketClient(this.socket, service) : super(service) {
     socket.listen((message) => onWebSocketMessage(message));
     socket.done.then((_) => close());
     service.subscribe('debug', this);
+    service.subscribe('gc', this);
   }
 
   void onWebSocketMessage(message) {
     if (message is String) {
       var map;
       try {
         map = JSON.decode(message);
       } catch (e) {
         socket.close(PARSE_ERROR_CODE, 'Message parse error: $e');
         return;
@@ skipping 165 matching lines @@
       _server = null;
       return this;
     }).catchError((e, st) {
       _server = null;
       print('Could not shutdown Observatory HTTP server:\n$e\n$st\n');
       return this;
     });
   }
 
 }