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

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 4c3c55a330e3b2851381770f874796130bca0b99..5d96bf424a18d897feb052e4ec1fd8cce97883eb 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2372,6 +2372,10 @@ const char kShelfChromeIconIndex[] = "shelf_chrome_icon_index";
 const char kPinnedLauncherApps[] = "pinned_launcher_apps";
 // Boolean value indicating whether to show a logout button in the ash tray.
 const char kShowLogoutButtonInTray[] = "show_logout_button_in_tray";
+// Integer value in milliseconds indicating the duration of logout confirmation
+// dialog after user pressed logout button. A value of 0 indicates to sign out
+// immediately without confirmation.
+const char kLogoutDialogDurationMs[] = "logout_dialog_duration_ms";
 // Dictionary value that holds per-display preference of shelf alignment and
 // auto-hide behavior. Key of the dictionary is the id of the display, and
 // its value is a dictionary whose keys are kShelfAlignment and