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

remoting/host/chromoting_host.cc

Index: remoting/host/chromoting_host.cc
diff --git a/remoting/host/chromoting_host.cc b/remoting/host/chromoting_host.cc
index 68009d493aec35b94183ba1eb3aae394aa44fc28..fc642e24eb84e3cb90676d4817eb72a3118c848a 100644
--- a/remoting/host/chromoting_host.cc
+++ b/remoting/host/chromoting_host.cc
@@ -267,15 +267,6 @@ void ChromotingHost::OnSessionRouteChange(
                                         route));
 }
 
-void ChromotingHost::OnClientResolutionChanged(ClientSession* session,
-                                               const SkISize& size,
-                                               const SkIPoint& dpi) {
-  DCHECK(network_task_runner_->BelongsToCurrentThread());
-  FOR_EACH_OBSERVER(HostStatusObserver, status_observers_,
-                    OnClientResolutionChanged(session->client_jid(),
-                                              size, dpi));
-}
-
 void ChromotingHost::OnSessionManagerReady() {
   DCHECK(network_task_runner_->BelongsToCurrentThread());
   // Don't need to do anything here, just wait for incoming