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

remoting/host/ipc_desktop_environment.cc

Index: remoting/host/ipc_desktop_environment.cc
diff --git a/remoting/host/ipc_desktop_environment.cc b/remoting/host/ipc_desktop_environment.cc
index 51ca9b16cd206081dcdbd2d39d8b23424a064218..71805d0be24e3d923c9020bd0d42f40368bfb531 100644
--- a/remoting/host/ipc_desktop_environment.cc
+++ b/remoting/host/ipc_desktop_environment.cc
@@ -18,6 +18,7 @@
 #include "remoting/host/desktop_session.h"
 #include "remoting/host/desktop_session_proxy.h"
 #include "remoting/host/event_executor.h"
+#include "remoting/host/session_controller.h"
 
 namespace remoting {
 
@@ -59,6 +60,13 @@ scoped_ptr<EventExecutor> IpcDesktopEnvironment::CreateEventExecutor(
                                                      ui_task_runner);
 }
 
+scoped_ptr<SessionController> IpcDesktopEnvironment::CreateSessionController() {
+  DCHECK(caller_task_runner_->BelongsToCurrentThread());
+
+  ConnectToDesktopSession();

[Jamie, 2013/03/09 00:53:18]

Why is this call needed for CreateSessionController but not for any of the other
Create* methods?

[alexeypa (please no reviews), 2013/03/09 01:05:34]

It is not needed. I guess I didn't pick one of fixes when I was preparing the
patch.

+  return desktop_session_proxy_->CreateSessionController();
+}
+
 scoped_ptr<media::ScreenCapturer> IpcDesktopEnvironment::CreateVideoCapturer(
     scoped_refptr<base::SingleThreadTaskRunner> capture_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> encode_task_runner) {