Realign message center popups when displays are added or removed

ui/message_center/views/desktop_popup_alignment_delegate.h

Index: ui/message_center/views/desktop_popup_alignment_delegate.h
diff --git a/ui/message_center/views/desktop_popup_alignment_delegate.h b/ui/message_center/views/desktop_popup_alignment_delegate.h
index 5c8cf43009bc5b4da37712515d04aeddc15eda15..fdf2aad717e4a72e45df9a8b1fad544a982991d4 100644
--- a/ui/message_center/views/desktop_popup_alignment_delegate.h
+++ b/ui/message_center/views/desktop_popup_alignment_delegate.h
@@ -49,6 +49,8 @@ class MESSAGE_CENTER_EXPORT DesktopPopupAlignmentDelegate
     POPUP_ALIGNMENT_RIGHT = 1 << 3,
   };
 
+  void UpdatePrimaryDisplay();
+
   // Overridden from display::DisplayObserver:
   void OnDisplayAdded(const display::Display& new_display) override;
   void OnDisplayRemoved(const display::Display& old_display) override;
@@ -56,7 +58,7 @@ class MESSAGE_CENTER_EXPORT DesktopPopupAlignmentDelegate
                                uint32_t metrics) override;
 
   int32_t alignment_;
-  int64_t display_id_;
+  int64_t primary_display_id_;
   display::Screen* screen_;
   gfx::Rect work_area_;