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

remoting/host/basic_desktop_environment.h

 // 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.
 
 #ifndef REMOTING_HOST_BASIC_DESKTOP_ENVIRONMENT_H_
 #define REMOTING_HOST_BASIC_DESKTOP_ENVIRONMENT_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
@@ skipping 11 matching lines @@
  public:
   explicit BasicDesktopEnvironment(bool use_x_damage);
   virtual ~BasicDesktopEnvironment();
 
   // DesktopEnvironment implementation.
   virtual scoped_ptr<AudioCapturer> CreateAudioCapturer(
       scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner) OVERRIDE;
   virtual scoped_ptr<EventExecutor> CreateEventExecutor(
       scoped_refptr<base::SingleThreadTaskRunner> input_task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) OVERRIDE;
+  virtual scoped_ptr<SessionController> CreateSessionController() OVERRIDE;
   virtual scoped_ptr<media::ScreenCapturer> CreateVideoCapturer(
       scoped_refptr<base::SingleThreadTaskRunner> capture_task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> encode_task_runner) OVERRIDE;
 
  private:
   // True if X DAMAGE support should be used by the video capturer.
   bool use_x_damage_;
 
   DISALLOW_COPY_AND_ASSIGN(BasicDesktopEnvironment);
 };
@@ skipping 13 matching lines @@
  private:
   // True if X DAMAGE support should be used by the video capturer.
   bool use_x_damage_;
 
   DISALLOW_COPY_AND_ASSIGN(BasicDesktopEnvironmentFactory);
 };
 
 }  // namespace remoting
 
 #endif  // REMOTING_HOST_BASIC_DESKTOP_ENVIRONMENT_H_