Make curtain-mode controllable by policy.

remoting/host/curtain_mode_mac.h

Index: remoting/host/curtain_mode_mac.h
diff --git a/remoting/host/curtain_mode_mac.h b/remoting/host/curtain_mode_mac.h
index 3d21805e81dff278fe9bec687fb3231171a12998..b439b1140fda341f36affbbf23361abe7b8e468f 100644
--- a/remoting/host/curtain_mode_mac.h
+++ b/remoting/host/curtain_mode_mac.h
@@ -17,27 +17,46 @@ namespace remoting {
 
 class CurtainMode : public HostStatusObserver {
  public:
-  CurtainMode();
+  // Set callbacks to be invoked when the switched-out session is switched back
+  // to the console, or in case of errors activating curtain-mode.  Typically,
+  // remote clients should be disconnected in both cases: for errors, because
+  // the privacy guarantee of curtain-mode cannot be honoured; for switch-in,
+  // to ensure that only one connection (console or remote) exists to a session.
+  // Note that only the session's owner (or someone who knows the password) can
+  // attach it to the console, so this is safe.
+  CurtainMode(const base::Closure& on_session_activate,
+              const base::Closure& on_error);
   virtual ~CurtainMode();
 
-  // Set the callback to be invoked when the switched-out remote session is
-  // switched back to the console.  Typically, remote connections should be
-  // closed in this event to make sure that only one connection (console or
-  // remote) exists to a session at any time to ensure privacy.  Note that
-  // only the session's owner (or someone who knows the owner's password)
-  // can attach it to the console, so this is safe.
-  bool Init(const base::Closure& on_session_activate);
+  // Enable or disable curtain-mode. Note that disabling curtain-mode does not
+  // deactivate the curtain, but it does remove the switch-in handler, meaning
+  // that on_session_activate will not be invoked if curtain-mode is disabled.
+  // Conversely, enabling curtain-mode *does* activate the curtain if there is
+  // a connected client at the time.
+  void SetEnabled(bool enabled);
 
   // Overridden from HostStatusObserver
   virtual void OnClientAuthenticated(const std::string& jid) OVERRIDE;
+  virtual void OnClientDisconnected(const std::string& jid) OVERRIDE;
 
  private:
+  // If the current session is attached to the console and is not showing
+  // the logon screen then switch it out to ensure privacy.
+  bool ActivateCurtain();
+
+  // Add or remove the switch-in event handler.
+  bool InstallEventHandler();
+  bool RemoveEventHandler();
+
+  // Handlers for the switch-in event.
   static OSStatus SessionActivateHandler(EventHandlerCallRef handler,
                                          EventRef event,
                                          void* user_data);
   void OnSessionActivate();
 
   base::Closure on_session_activate_;
+  base::Closure on_error_;
+  bool connection_active_;
   EventHandlerRef event_handler_;
 };