Call the DisconnectWindow interface methods on the UI thread.

remoting/host/chromoting_host.h

Index: remoting/host/chromoting_host.h
diff --git a/remoting/host/chromoting_host.h b/remoting/host/chromoting_host.h
index 20d476ad0585c0fc9b88b50125ec5942b64dc163..a5d83db3bd0fbfa059a001c31149fa508fbfab51 100644
--- a/remoting/host/chromoting_host.h
+++ b/remoting/host/chromoting_host.h
@@ -166,6 +166,10 @@ class ChromotingHost : public base::RefCountedThreadSafe<ChromotingHost>,
   void ProcessPreAuthentication(
       const scoped_refptr<protocol::ConnectionToClient>& connection);
 
+  // Show or hide the Disconnect window on the UI thread.  If |show| is false,
+  // hide the window, ignoring the |username| parameter.
+  void ShowDisconnectWindow(bool show, const std::string& username);
+
   // The context that the chromoting host runs on.
   ChromotingHostContext* context_;