Overlay scrollbars expand only when mouse is near thumb

cc/input/scrollbar_animation_controller.h

 // Copyright 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 CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 58 matching lines @@
   // DidScrollUpdate expects to be called only if the scroll position change.
   // Effect both Android and Aura Overlay Scrollbar.
   void DidScrollUpdate();
 
   void DidScrollBegin();
   void DidScrollEnd();
 
   void DidMouseDown();
   void DidMouseUp();
   void DidMouseLeave();
-  void DidMouseMoveNear(ScrollbarOrientation, float);
+  void DidMouseMove(const gfx::PointF& device_viewport_point);
 
   // Called when Blink wants to show the scrollbars (via
   // ScrollableArea::showOverlayScrollbars).
   void DidRequestShowFromMainThread();
 
-  bool MouseIsOverScrollbar(ScrollbarOrientation orientation) const;
+  // These methods are public for testing.
+  bool MouseIsOverScrollbarThumb(ScrollbarOrientation orientation) const;
+  bool MouseIsNearScrollbarThumb(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearAnyScrollbar() const;
 
   static constexpr float kMouseMoveDistanceToTriggerFadeIn = 30.0f;
 
  private:
   // Describes whether the current animation should FadeIn or FadeOut.
   enum AnimationChange { NONE, FADE_IN, FADE_OUT };
 
   ScrollbarAnimationController(ElementId scroll_element_id,
@@ skipping 18 matching lines @@
 
   void StartAnimation();
   void StopAnimation();
 
   void Show();
 
   void PostDelayedAnimation(AnimationChange animation_change);
 
   bool Captured() const;
 
-  bool CalcNeedTriggerScrollbarShow(ScrollbarOrientation orientation,
-                                    float distance) const;
-
   void ApplyOpacityToScrollbars(float opacity);
 
   ScrollbarAnimationControllerClient* client_;
 
   base::TimeTicks last_awaken_time_;
 
   base::TimeDelta fade_delay_;
 
   base::TimeDelta fade_duration_;
 
-  bool need_trigger_scrollbar_show_;
+  bool need_trigger_scrollbar_fade_in_;
 
   bool is_animating_;
   AnimationChange animation_change_;
 
   const ElementId scroll_element_id_;
   bool currently_scrolling_;
   bool show_in_fast_scroll_;
 
   base::CancelableClosure delayed_scrollbar_animation_;
 
   float opacity_;
 
   const bool show_scrollbars_on_scroll_gesture_;
   const bool need_thinning_animation_;
+
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       vertical_controller_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       horizontal_controller_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_