ResizingHostObserver is created by the desktop environment together with other stubs.

remoting/host/basic_desktop_environment.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "remoting/host/basic_desktop_environment.h"
 
 #include "base/logging.h"
 #include "media/video/capture/screen/screen_capturer.h"
 #include "remoting/host/audio_capturer.h"
+#include "remoting/host/desktop_resizer.h"
 #include "remoting/host/event_executor.h"
+#include "remoting/host/resizing_host_observer.h"
 
 namespace remoting {
 
 BasicDesktopEnvironment::BasicDesktopEnvironment(bool use_x_damage)
     : use_x_damage_(use_x_damage) {
 }
 
 BasicDesktopEnvironment::~BasicDesktopEnvironment() {
   DCHECK(CalledOnValidThread());
 }
 
 scoped_ptr<AudioCapturer> BasicDesktopEnvironment::CreateAudioCapturer(
     scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner) {
   DCHECK(CalledOnValidThread());
 
   return AudioCapturer::Create();
 }
 
 scoped_ptr<EventExecutor> BasicDesktopEnvironment::CreateEventExecutor(
     scoped_refptr<base::SingleThreadTaskRunner> input_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
   DCHECK(CalledOnValidThread());
 
   return EventExecutor::Create(input_task_runner, ui_task_runner);
 }
 
+scoped_ptr<SessionController>
+BasicDesktopEnvironment::CreateSessionController() {
+  DCHECK(CalledOnValidThread());
+
+  scoped_ptr<SessionController> session_controller(
+      new ResizingHostObserver(DesktopResizer::Create()));
+  return session_controller.Pass();
+}
+
 scoped_ptr<media::ScreenCapturer> BasicDesktopEnvironment::CreateVideoCapturer(
     scoped_refptr<base::SingleThreadTaskRunner> capture_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> encode_task_runner) {
   DCHECK(CalledOnValidThread());
 
 #if defined(OS_LINUX)
   return media::ScreenCapturer::CreateWithXDamage(use_x_damage_);
 #else  // !defined(OS_LINUX)
   return media::ScreenCapturer::Create();
 #endif  // !defined(OS_LINUX)
@@ skipping 12 matching lines @@
     const base::Closure& disconnect_callback) {
   return scoped_ptr<DesktopEnvironment>(
       new BasicDesktopEnvironment(use_x_damage_));
 }
 
 bool BasicDesktopEnvironmentFactory::SupportsAudioCapture() const {
   return AudioCapturer::IsSupported();
 }
 
 }  // namespace remoting