Prevent overlay scrollbars expand or hover together

cc/input/scrollbar_animation_controller_thinning.h

Index: cc/input/scrollbar_animation_controller_thinning.h
diff --git a/cc/input/scrollbar_animation_controller_thinning.h b/cc/input/scrollbar_animation_controller_thinning.h
index 236e595ea263ec5d9f090d913005b34bfbbcd967..cf0626447e0dfb139e41b0c12a69e3d65be32805 100644
--- a/cc/input/scrollbar_animation_controller_thinning.h
+++ b/cc/input/scrollbar_animation_controller_thinning.h
@@ -10,11 +10,17 @@
 #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.

[bokan, 2017/01/20 18:57:25]

Add to this comment an explanation of how this class works, that the fade out
works on both scrollbars and is controlled in this class. The thinning
animations are independent between vertical/horizontal and are managed by the
SingleScrollbarControllers.

+
+// 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:
@@ -28,22 +34,23 @@ class CC_EXPORT ScrollbarAnimationControllerThinning
 
   ~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,
@@ -52,38 +59,21 @@ class CC_EXPORT ScrollbarAnimationControllerThinning
       base::TimeDelta fade_duration,
       base::TimeDelta thinning_duration);
 
-  void RunAnimationFrame(float progress) override;
-  const base::TimeDelta& Duration() override;
+  SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
+      ScrollbarOrientation) const;
 
- 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);
+  bool Captured() const;
+  void RunAnimationFrame(float progress) override;
+  const base::TimeDelta& Duration() override;
 
-  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);
 };