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 64 matching lines @@
   // DidResize expects to be called when clip layer size changed or scroll layer
   // size changed.
   void DidResize();
 
   void DidScrollBegin();
   void DidScrollEnd();
 
   void DidMouseDown();
   void DidMouseUp();
   void DidMouseLeave();
-  void DidMouseMoveNear(ScrollbarOrientation, float);
+  void DidMouseMoveNear(ScrollbarOrientation orientation,
+                        const gfx::PointF& device_viewport_point);
 
   // Called when Blink wants to show the scrollbars (via
   // ScrollableArea::showOverlayScrollbars).
   void DidRequestShowFromMainThread();
 
-  bool MouseIsOverScrollbar(ScrollbarOrientation orientation) const;
+  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,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
                                base::TimeDelta fade_out_resize_delay,
                                base::TimeDelta fade_duration);
 
   ScrollbarAnimationController(ElementId scroll_element_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_delay,
                                base::TimeDelta fade_out_resize_delay,
                                base::TimeDelta fade_duration,
                                base::TimeDelta thinning_duration);
 
   ScrollbarSet Scrollbars() const;
+  ScrollbarLayerImplBase* GetScrollbar(ScrollbarOrientation orientation) const;
   SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
       ScrollbarOrientation) const;
 
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
   void RunAnimationFrame(float progress);
 
   void StartAnimation();
   void StopAnimation();
@@ skipping 37 matching lines @@
       vertical_controller_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       horizontal_controller_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_