Prevent overlay scrollbars expand or hover together

cc/input/scrollbar_animation_controller_thinning.h

 // Copyright 2013 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_THINNING_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar_animation_controller.h"
+#include "cc/input/single_scrollbar_animation_controller_thinning.h"
 
 namespace cc {
 
-// Scrollbar animation that partially fades and thins after an idle delay,
-// and reacts to mouse movements.
+// This class fade in scrollbars when scroll and fade out after an idle delay.
+// The fade animations works on both scrollbars and is controlled in this class.
+// This class It passes the mouse state to each

[bokan, 2017/01/20 19:58:32]

Nit: "class It passes" -> "class passes"

+// SingleScrollbarAnimationControllerThinning. The thinning animations are
+// independent between vertical/horizontal and are managed by the
+// SingleScrollbarAnimationControllerThinnings.
+
+// TODO(chaopeng) clean up the inheritance hierarchy after
+// ScrollbarAnimationControllerLinearFade merge into
+// ScrollbarAnimationControllerThinning so we can remove the empty overrides and
+// NOTREACHED() checks.
 class CC_EXPORT ScrollbarAnimationControllerThinning
     : public ScrollbarAnimationController {
  public:
   static std::unique_ptr<ScrollbarAnimationControllerThinning> Create(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
       base::TimeDelta resize_delay_before_starting,
       base::TimeDelta fade_duration,
       base::TimeDelta thinning_duration);
 
   ~ScrollbarAnimationControllerThinning() override;
 
-  void set_mouse_move_distance_for_test(float distance) {
-    mouse_move_distance_to_trigger_animation_ = distance;
-  }
-  bool mouse_is_over_scrollbar() const { return mouse_is_over_scrollbar_; }
-  bool mouse_is_near_scrollbar() const { return mouse_is_near_scrollbar_; }
+  void set_mouse_move_distance_for_test(float distance);
 
+  bool mouse_is_over_scrollbar(ScrollbarOrientation orientation) const;
+  bool mouse_is_near_scrollbar(ScrollbarOrientation orientation) const;
+  bool mouse_is_near_any_scrollbar() const;
+
+  bool Animate(base::TimeTicks now) override;
   void DidScrollUpdate(bool on_resize) override;
   void DidScrollEnd() override;
-
   void DidMouseDown() override;
   void DidMouseUp() override;
   void DidMouseLeave() override;
-  void DidMouseMoveNear(float distance) override;
+  void DidMouseMoveNear(ScrollbarOrientation orientation,
+                        float distance) override;
   bool ScrollbarsHidden() const override;
 
- protected:
+ private:
   ScrollbarAnimationControllerThinning(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
       base::TimeDelta resize_delay_before_starting,
       base::TimeDelta fade_duration,
       base::TimeDelta thinning_duration);
 
+  SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
+      ScrollbarOrientation) const;
+
+  void ApplyOpacity(float opacity);
+  bool Captured() const;
   void RunAnimationFrame(float progress) override;
   const base::TimeDelta& Duration() override;
 
- private:
-  // Describes whether the current animation should INCREASE (thicken)
-  // a bar or DECREASE it (thin).
-  enum AnimationChange { NONE, INCREASE, DECREASE };
-  enum AnimatingProperty { OPACITY, THICKNESS };
-  float ThumbThicknessScaleAt(float progress);
-  float AdjustScale(float new_value,
-                    float current_value,
-                    AnimationChange animation_change,
-                    float min_value,
-                    float max_value);
-  void ApplyOpacity(float opacity);
-  void ApplyThumbThicknessScale(float thumb_thickness_scale);
-
-  void SetCurrentAnimatingProperty(AnimatingProperty property);
+  std::unique_ptr<SingleScrollbarAnimationControllerThinning>
+      vertical_controller_;
+  std::unique_ptr<SingleScrollbarAnimationControllerThinning>
+      horizontal_controller_;
 
   float opacity_;
-  bool captured_;
-  bool mouse_is_over_scrollbar_;
-  bool mouse_is_near_scrollbar_;
-  // Are we narrowing or thickening the bars.
-  AnimationChange thickness_change_;
-  // How close should the mouse be to the scrollbar before we thicken it.
-  float mouse_move_distance_to_trigger_animation_;
-
   base::TimeDelta fade_duration_;
-  base::TimeDelta thinning_duration_;
-
-  AnimatingProperty current_animating_property_;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarAnimationControllerThinning);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_