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..ad732e8be313c93fcb7e12dd728bf44fe4707e6f 100644
--- a/ash/system/logout_button/logout_button_observer.h
+++ b/ash/system/logout_button/logout_button_observer.h
@@ -7,14 +7,20 @@
 
 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 value of the kShowLogoutButtonInTray pref and

[bartfab (slow), 2013/10/28 16:24:07]

Nit: s/value/values/

[binjin, 2013/10/29 16:07:05]

Done.

+// kLogoutDialogDurationMs pref. kShowLogoutButtonInTray determines whether a

[bartfab (slow), 2013/10/28 16:24:07]

Nit: s/pref/prefs/

[binjin, 2013/10/29 16:07:05]

Done.

+// 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(int duration) = 0;

[bartfab (slow), 2013/10/28 16:24:07]

Instead of an int, use a base::TimeDelta here.

[binjin, 2013/10/29 16:07:05]

I think the interface should be aware of the type preference only, assigning
high level types is not proper here. If I use base::TimeDelta here I had to do
the conversation in a lower level which is not proper I think.

 };
 
 }  // namespace ash