[Notifications] Fix swipe to close for ARC notifications.

ui/message_center/views/slide_out_controller.h

 // Copyright (c) 2012 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_MESSAGE_CENTER_VIEWS_SLIDE_OUT_CONTROLLER_H_
 #define UI_MESSAGE_CENTER_VIEWS_SLIDE_OUT_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/events/scoped_target_handler.h"
 #include "ui/views/view.h"
 #include "ui/views/views_export.h"
 
 namespace views {
 
 // This class contains logic to control sliding out of a layer in response to
 // swipes, i.e. gesture scroll events.
 class SlideOutController : public ui::EventHandler,
                            public ui::ImplicitAnimationObserver {
  public:
   class Delegate {
    public:
     // Returns the layer for slide operations.
     virtual ui::Layer* GetSlideOutLayer() = 0;
 
+    // Called when a slide starts, ends, or is updated.
+    virtual void OnSlideChanged() = 0;
+
     // Called when user intends to close the View by sliding it out.
     virtual void OnSlideOut() = 0;
   };
 
   SlideOutController(ui::EventTarget* target, Delegate* delegate);
   ~SlideOutController() override;
 
   void set_enabled(bool enabled) { enabled_ = enabled; }
   bool enabled() { return enabled_; }
 
@@ skipping 16 matching lines @@
 
   float gesture_amount_ = 0.f;
   bool enabled_ = true;
 
   DISALLOW_COPY_AND_ASSIGN(SlideOutController);
 };
 
 }  // namespace views
 
 #endif  // UI_MESSAGE_CENTER_VIEWS_SLIDE_OUT_CONTROLLER_H_