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

remoting/host/ipc_session_controller.h

+// Copyright (c) 2013 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_IPC_SESSION_CONTROLLER_H_
+#define REMOTING_HOST_IPC_SESSION_CONTROLLER_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "remoting/host/session_controller.h"
+
+namespace remoting {
+
+class DesktopSessionProxy;
+
+class IpcSessionController : public SessionController {
+ public:
+  explicit IpcSessionController(
+      scoped_refptr<DesktopSessionProxy> desktop_session_proxy);
+  virtual ~IpcSessionController();
+
+  // SessionController interface.
+  virtual void OnClientResolutionChanged(const SkIPoint& client_dpi,
+                                         const SkISize& client_size) OVERRIDE;
+
+ private:
+  // Wraps the IPC channel to the desktop session agent.
+  scoped_refptr<DesktopSessionProxy> desktop_session_proxy_;
+
+  DISALLOW_COPY_AND_ASSIGN(IpcSessionController);
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_IPC_SESSION_CONTROLLER_H_