Crash the network or desktop process when an unknown IPC message is received.

remoting/host/desktop_session_proxy.cc

Index: remoting/host/desktop_session_proxy.cc
diff --git a/remoting/host/desktop_session_proxy.cc b/remoting/host/desktop_session_proxy.cc
index 55f7fc597df2d4f4ff9ab5b4185dd584fbf81fb3..44b213f53b48c720784816a8959684ebc3884213 100644
--- a/remoting/host/desktop_session_proxy.cc
+++ b/remoting/host/desktop_session_proxy.cc
@@ -94,6 +94,8 @@ bool DesktopSessionProxy::OnMessageReceived(const IPC::Message& message) {
                         DisconnectSession);
   IPC_END_MESSAGE_MAP()
 
+  CHECK(handled) << "An unexpected IPC message received: type="
+                 << message.type();
   return handled;
 }