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 1144e7241b0ec572b94a8bdd8a24bc86d4d02287..38e5fa8344903ee5e9e61e8db1df0c865891a85a 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -2433,6 +2433,11 @@ 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 length of time for which a
+// confirmation dialog should be shown when the user presses the logout button.
+// A value of 0 indicates that logout should happen immediately, without showing
+// a confirmation dialog.
+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