Add SessionStateObserver with ActiveUserChanged()

ash/system/user/tray_user.cc

Index: ash/system/user/tray_user.cc
diff --git a/ash/system/user/tray_user.cc b/ash/system/user/tray_user.cc
index e3c0697a9c4321d3f3b116f9831efed0de9c008f..3da03a99f83522f7209884afefb884e3ad3a1fe8 100644
--- a/ash/system/user/tray_user.cc
+++ b/ash/system/user/tray_user.cc
@@ -273,6 +273,9 @@ class UserView : public views::View,
   // The view of the user card.
   views::View* user_card_view_;
 
+  // This is the owner system tray item of this view.
+  SystemTrayItem* owner_;
+
   // True if |user_card_view_| is a |UserView| - otherwise it is only a
   // |views::View|.
   bool is_user_card_;
@@ -595,6 +598,7 @@ UserView::UserView(SystemTrayItem* owner,
                    MultiProfileIndex index)
     : multiprofile_index_(index),
       user_card_view_(NULL),
+      owner_(owner),

[Mr4D (OOO till 08-26), 2013/05/31 22:23:39]

Instead of passing the owner you might consider to use:

GetRootWindowController(Shell::GetActiveRootWindow())->shelf()->status_area_widget()->system_tray();

But then again - the other tray items are doing it the same way, so this should
be fine.

[bartfab (slow), 2013/06/03 09:00:06]

|owner_| will continue to work if/when we have multiple system trays one day,
singleton accesses will not.

[Nikita (slow), 2013/06/03 09:21:28]

Leaving as is then to follow existing pattern and to address this concern.

       is_user_card_(false),
       logout_button_(NULL),
       add_user_visible_but_disabled_(false) {
@@ -710,6 +714,8 @@ void UserView::ButtonPressed(views::Button* sender, const ui::Event& event) {
       ash::SessionStateDelegate* delegate =
           ash::Shell::GetInstance()->session_state_delegate();
       delegate->SwitchActiveUser(delegate->GetUserEmail(multiprofile_index_));
+      // User list will change and it makes sense to close bubble.

[Mr4D (OOO till 08-26), 2013/05/31 22:23:39]

Since the user list is about to change the system menu should get closed.

[Nikita (slow), 2013/06/03 09:21:28]

Done.

+      owner_->system_tray()->CloseSystemBubble();
     }
   } else if (add_menu_option_.get() &&
              sender == add_menu_option_->GetContentsView()) {