Add a VM page to the observatory.

runtime/bin/vmservice/client/lib/src/app/application.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 app;
 
 /// A request response interceptor is called for each response.
 typedef void RequestResponseInterceptor();
 
 /// The observatory application. Instances of this are created and owned
 /// by the observatory_application custom element.
 class ObservatoryApplication extends Observable {
   @observable final LocationManager locationManager;
   @observable final VM vm;
   @observable Isolate isolate;
+
+  /// The current [ServiceObject] being viewed by the application.
   @observable ServiceObject response;
 
-  void setResponse(ServiceObject response) {
-    this.response = response;
-  }
+  /// Any client-level arguments for viewing the current response.
+  @observable String args;
+  // TODO(turnidge): Make args a Map.
 
   void _initOnce() {
     // Only called once.
     assert(locationManager._app == null);
     locationManager._app = this;
     locationManager.init();
   }
 
   ObservatoryApplication.devtools() :
       locationManager = new LocationManager(),
       vm = new DartiumVM() {
     _initOnce();
   }
 
   ObservatoryApplication() :
       locationManager = new LocationManager(),
       vm = new HttpVM('http://127.0.0.1:8181/') {
     _initOnce();
   }
 }