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..17cba929b643524fefbedbdf472b26ac07e8ea80 100644
--- a/ash/system/logout_button/logout_button_observer.h
+++ b/ash/system/logout_button/logout_button_observer.h
@@ -5,16 +5,23 @@
 #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.
 class LogoutButtonObserver {
  public:
   virtual ~LogoutButtonObserver() {}
 
-  // Called when the value of the kShowLogoutButtonInTray pref changes.
+  // Called when the value of the kShowLogoutButtonInTray pref changes, which
+  // determines whether a logout button should be shown in the system tray
+  // during a session.
   virtual void OnShowLogoutButtonInTrayChanged(bool show) = 0;
+
+  // Called when the value of the kLogoutDialogDurationMs pref changes.
+  // 'duration' is the duration of the logout confirmation dialog after user

[bartfab (slow), 2013/12/03 19:46:04]

Nit 1: We use | to delimit argument names, so |duration|.

Nit 2: Wording: s/of the logout confirmation dialog after user pressed logout
button/for which the logout confirmation dialog is shown after the user has
pressed the logout button/

[binjin, 2013/12/04 10:47:03]

Done.

+  // pressed logout button.
+  virtual void OnLogoutDialogDurationChanged(base::TimeDelta duration) = 0;
 };
 
 }  // namespace ash