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

ash/system/logout_button/logout_button_tray.h

Index: ash/system/logout_button/logout_button_tray.h
diff --git a/ash/system/logout_button/logout_button_tray.h b/ash/system/logout_button/logout_button_tray.h
index 5683e5e2654c13f52e1d2e9efe0a9403e91b9cf2..f0617f04002e028e781c0a955438c825e435cabd 100644
--- a/ash/system/logout_button/logout_button_tray.h
+++ b/ash/system/logout_button/logout_button_tray.h
@@ -20,6 +20,7 @@ namespace ash {
 namespace internal {
 
 class StatusAreaWidget;
+class LogoutConfirmationDialogView;
 
 // Adds a logout button to the launcher's status area if enabled by the
 // kShowLogoutButtonInTray pref.
@@ -30,6 +31,10 @@ class LogoutButtonTray : public TrayBackgroundView,
   explicit LogoutButtonTray(StatusAreaWidget* status_area_widget);
   virtual ~LogoutButtonTray();
 
+  void ShowConfirmDialog();

[bartfab (slow), 2013/10/24 13:11:02]

- Here and elsewhere: s/confirm/confirmation/
- All three methods: Why public, not private?

[binjin, 2013/10/25 13:03:10]

They are supposed to be accessed by LogoutConfirmationDialogView, and they are
already in ash::internal namespace.

+  void CloseConfirmDialog();
+  void RemoveConfirmDialogInstance(LogoutConfirmationDialogView *instance);
+
   // TrayBackgroundView:
   virtual void SetShelfAlignment(ShelfAlignment alignment) OVERRIDE;
   virtual base::string16 GetAccessibleNameForTray() OVERRIDE;
@@ -53,6 +58,8 @@ class LogoutButtonTray : public TrayBackgroundView,
   user::LoginStatus login_status_;
   bool show_logout_button_in_tray_;
 
+  LogoutConfirmationDialogView* confirm_dialog_;

[bartfab (slow), 2013/10/24 13:11:02]

As commented in logout_confirmation_dialog_view.cc, I think this should be a
base::WeakPtr.

[binjin, 2013/10/25 13:03:10]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(LogoutButtonTray);
 };