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

chrome/browser/ui/ash/chrome_launcher_prefs.cc

Index: chrome/browser/ui/ash/chrome_launcher_prefs.cc
diff --git a/chrome/browser/ui/ash/chrome_launcher_prefs.cc b/chrome/browser/ui/ash/chrome_launcher_prefs.cc
index e7f9f3b8005803fb3d274d3d57c651f0d8537194..cdf8facf5b3115aadf4adacb6c534eaf6df4a2c4 100644
--- a/chrome/browser/ui/ash/chrome_launcher_prefs.cc
+++ b/chrome/browser/ui/ash/chrome_launcher_prefs.cc
@@ -83,6 +83,10 @@ void RegisterChromeLauncherUserPrefs(
       prefs::kShowLogoutButtonInTray,
       false,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterIntegerPref(
+      prefs::kLogoutDialogDurationMs,
+      20000,
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterDictionaryPref(
       prefs::kShelfPreferences,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);