Implements the dialog view for logout button tray in public sessions.

ash/system/logout_button/logout_button_observer.h

Index: ash/system/logout_button/logout_button_observer.h
diff --git a/ash/system/logout_button/logout_button_observer.h b/ash/system/logout_button/logout_button_observer.h
index 9234c7d758d9c80b13ab2526543ddc2a035655a1..1d1d721cdac421d864dc5a68566f406a1368830b 100644
--- a/ash/system/logout_button/logout_button_observer.h
+++ b/ash/system/logout_button/logout_button_observer.h
@@ -5,16 +5,24 @@
 #ifndef ASH_SYSTEM_LOGOUT_BUTTON_LOGOUT_BUTTON_OBSERVER_H_
 #define ASH_SYSTEM_LOGOUT_BUTTON_LOGOUT_BUTTON_OBSERVER_H_
 
+#include "base/time/time.h"
+
 namespace ash {
 
-// Observer for the value of the kShowLogoutButtonInTray pref that determines
-// whether a logout button should be shown in the system tray during a session.
+// Observer for the values of the kShowLogoutButtonInTray pref and

[bartfab (slow), 2013/11/20 18:00:44]

Nit 1: s/pref//

Nit 2: The reference to kShowLogoutButtonInTray made sense before because this
class really just tracked a pref 1:1. Now it tracks two things and one is a
base::TimeDelta derived from a pref, not just a raw pref value. I think you can
reword the entire description and remove the references to prefs by name. It
makes sense to keep them in the comments above the individual methods though so
it is clear when exactly they get called.

+// kLogoutDialogDurationMs prefs. kShowLogoutButtonInTray determines whether a
+// logout button should be shown in the system tray during a session.
+// kLogoutDialogDurationMs is the duration in milliseconds of the logout
+// confirmation dialog after user pressed logout button.
 class LogoutButtonObserver {
  public:
   virtual ~LogoutButtonObserver() {}
 
   // Called when the value of the kShowLogoutButtonInTray pref changes.
   virtual void OnShowLogoutButtonInTrayChanged(bool show) = 0;
+
+  // Called when the value of the kLogoutDialogDurationMs pref changes.
+  virtual void OnLogoutDialogDurationChanged(base::TimeDelta duration) = 0;
 };
 
 }  // namespace ash