Adjust behavior of control buttons of notifications.

ui/message_center/views/message_center_view.h

Index: ui/message_center/views/message_center_view.h
diff --git a/ui/message_center/views/message_center_view.h b/ui/message_center/views/message_center_view.h
index da206b0ca08b845ee7c4163d1425c182e1774ff0..60f9d73d8fb9ab0e88abac13ce4ad25377d1b492 100644
--- a/ui/message_center/views/message_center_view.h
+++ b/ui/message_center/views/message_center_view.h
@@ -15,6 +15,7 @@
 #include "ui/message_center/views/message_center_controller.h"
 #include "ui/message_center/views/message_list_view.h"
 #include "ui/message_center/views/message_view.h"
+#include "ui/views/focus/focus_manager.h"
 #include "ui/views/view.h"
 
 namespace gfx {
@@ -40,7 +41,8 @@ class MESSAGE_CENTER_EXPORT MessageCenterView
       public MessageCenterObserver,
       public MessageCenterController,
       public MessageListView::Observer,
-      public gfx::AnimationDelegate {
+      public gfx::AnimationDelegate,
+      public views::FocusChangeListener {
  public:
   MessageCenterView(MessageCenter* message_center,
                     MessageCenterTray* tray,
@@ -48,6 +50,8 @@ class MESSAGE_CENTER_EXPORT MessageCenterView
                     bool initially_settings_visible);
   ~MessageCenterView() override;
 
+  void Init();
+
   void SetNotifications(const NotificationList::Notifications& notifications);
 
   void ClearAllClosableNotifications();
@@ -61,6 +65,10 @@ class MESSAGE_CENTER_EXPORT MessageCenterView
 
   void SetIsClosing(bool is_closing);
 
+  // Overridden from views::FocusChangeListener
+  void OnWillChangeFocus(views::View* before, views::View* now) override {}
+  void OnDidChangeFocus(views::View* before, views::View* now) override;
+
  protected:
   // Potentially sets the reposition target, and then returns whether or not it
   // was was set.
@@ -155,6 +163,8 @@ class MESSAGE_CENTER_EXPORT MessageCenterView
 
   std::unique_ptr<MessageViewContextMenuController> context_menu_controller_;
 
+  views::FocusManager* focus_manager_ = nullptr;
+
   DISALLOW_COPY_AND_ASSIGN(MessageCenterView);
 };