Put the close button of a notification into focus chain.

ui/arc/notification/arc_custom_notification_view.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 #define UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "ui/arc/notification/arc_custom_notification_item.h"
 #include "ui/arc/notification/arc_notification_surface_manager.h"
 #include "ui/aura/window_observer.h"
 #include "ui/message_center/views/custom_notification_content_view_delegate.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/native/native_view_host.h"
 
 namespace exo {
 class NotificationSurface;
 }
 
 namespace views {
+class FocusTraversable;
 class ImageButton;
 class Widget;
 }
 
 namespace arc {
 
 class ArcCustomNotificationView
     : public views::NativeViewHost,
       public views::ButtonListener,
       public aura::WindowObserver,
       public ArcCustomNotificationItem::Observer,
       public ArcNotificationSurfaceManager::Observer {
  public:
   explicit ArcCustomNotificationView(ArcCustomNotificationItem* item);
   ~ArcCustomNotificationView() override;
 
   std::unique_ptr<message_center::CustomNotificationContentViewDelegate>
   CreateContentViewDelegate();
 
  private:
   class ContentViewDelegate;
+  class CloseButton;
   class EventForwarder;
   class SlideHelper;
 
   void CreateFloatingCloseButton();
   void SetSurface(exo::NotificationSurface* surface);
   void UpdatePreferredSize();
   void UpdateCloseButtonVisiblity();
   void UpdatePinnedState();
   void UpdateSnapshot();
   void AttachSurface();
 
   // views::NativeViewHost
   void ViewHierarchyChanged(
       const ViewHierarchyChangedDetails& details) override;
   void Layout() override;
   void OnPaint(gfx::Canvas* canvas) override;
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
   void OnMouseEntered(const ui::MouseEvent& event) override;
   void OnMouseExited(const ui::MouseEvent& event) override;
   void OnFocus() override;
   void OnBlur() override;
+  views::FocusTraversable* GetFocusTraversable() override;
 
   // views::ButtonListener
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   // aura::WindowObserver
   void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
   void OnWindowDestroying(aura::Window* window) override;
 
@@ skipping 31 matching lines @@
 
   // Protects from call loops between Layout and OnWindowBoundsChanged.
   bool in_layout_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(ArcCustomNotificationView);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_