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 0b393088b89c209f5771c617781c4bce7a264f89..425dabaeaadc5e6221d5048ffb0eac8cfe4bfa2c 100644
--- a/cc/input/scrollbar_animation_controller_thinning.h
+++ b/cc/input/scrollbar_animation_controller_thinning.h
@@ -5,20 +5,24 @@
 #ifndef CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 
+#include <algorithm>

[bokan, 2016/12/08 19:34:07]

I think this is unneeded?

 #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 {
 
+using std::unique_ptr;

[bokan, 2016/12/08 19:34:07]

I would prefer just using std:: in the declarations.

+
 // Scrollbar animation that partially fades and thins after an idle delay,
 // and reacts to mouse movements.
 class CC_EXPORT ScrollbarAnimationControllerThinning

[bokan, 2016/12/08 19:34:07]

Please file a bug and add a TODO to clean up the inheritance hierarchy here. The
reason we have an abstract ScrollbarAnimationController is because we have the
thinning and fade versions of SAC. Issue 656606 (you can block the new bug on
this one) tracks merging the fade version into this one. Once we do that,
there's no reason for the SingleScrollbarAnimationControllerThinning to be
related to ScrollbarAnimationControllerThinning so we can remove the empty
overrides and NOTREACHED() checks. 

     : public ScrollbarAnimationController {
  public:
-  static std::unique_ptr<ScrollbarAnimationControllerThinning> Create(
+  static unique_ptr<ScrollbarAnimationControllerThinning> Create(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
@@ -28,19 +32,18 @@ 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);
 
-  void DidScrollUpdate(bool on_resize) override;
+  bool mouse_is_over_scrollbar(ScrollbarOrientation orientation) const;
+  bool mouse_is_near_scrollbar(ScrollbarOrientation orientation) const;
+  bool ScrollbarsHidden() const override;
 
+  bool Animate(base::TimeTicks now) override;
+  void DidScrollUpdate(bool on_resize) override;
   void DidMouseDown() override;
   void DidMouseUp() override;
   void DidMouseLeave() override;
-  void DidMouseMoveNear(float distance) override;
-  bool ScrollbarsHidden() const override;
+  void DidMouseMoveNear(ScrollbarOrientation, float) override;
 
  protected:
   ScrollbarAnimationControllerThinning(
@@ -55,34 +58,11 @@ class CC_EXPORT ScrollbarAnimationControllerThinning
   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);
-
-  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_;
+  unique_ptr<SingleScrollbarAnimationControllerThinning> v_scrollbar_controller;
+  unique_ptr<SingleScrollbarAnimationControllerThinning> h_scrollbar_controller;

[bokan, 2016/12/08 19:34:07]

Call these vertical_controller_ and horizontal_controller_. Don't forget the
trailing _.

+
+  SingleScrollbarAnimationControllerThinning* GetScrollbarAnimationController(
+      ScrollbarOrientation) const;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollbarAnimationControllerThinning);
 };