Prevent overlay scrollbars expand or hover together

cc/input/scrollbar_animation_controller.h

Index: cc/input/scrollbar_animation_controller.h
diff --git a/cc/input/scrollbar_animation_controller.h b/cc/input/scrollbar_animation_controller.h
index bb3f810a4c2269d58267730ea97694916de2a899..bdfc2f8808a89ec48fa984a018031b367e47e0ae 100644
--- a/cc/input/scrollbar_animation_controller.h
+++ b/cc/input/scrollbar_animation_controller.h
@@ -9,6 +9,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
+#include "cc/input/scrollbar.h"

[bokan, 2016/12/21 15:56:02]

Not used.

 #include "cc/layers/layer_impl.h"
 #include "cc/layers/scrollbar_layer_impl_base.h"
 #include "ui/gfx/geometry/vector2d_f.h"
@@ -37,7 +38,7 @@ class CC_EXPORT ScrollbarAnimationController {
  public:
   virtual ~ScrollbarAnimationController();
 
-  bool Animate(base::TimeTicks now);
+  virtual bool Animate(base::TimeTicks now);
 
   virtual void DidScrollBegin();
   virtual void DidScrollUpdate(bool on_resize);
@@ -45,7 +46,7 @@ class CC_EXPORT ScrollbarAnimationController {
   virtual void DidMouseDown() {}
   virtual void DidMouseUp() {}
   virtual void DidMouseLeave() {}
-  virtual void DidMouseMoveNear(float distance) {}
+  virtual void DidMouseMoveNear(ScrollbarOrientation, float) {}
   virtual bool ScrollbarsHidden() const;
 
  protected:
@@ -59,6 +60,7 @@ class CC_EXPORT ScrollbarAnimationController {
 
   void StartAnimation();
   void StopAnimation();
+
   ScrollbarSet Scrollbars() const;
 
   ScrollbarAnimationControllerClient* client_;
@@ -67,6 +69,10 @@ class CC_EXPORT ScrollbarAnimationController {
 
   int scroll_layer_id() const { return scroll_layer_id_; }
 
+  bool animating() const { return is_animating_; }

[bokan, 2016/12/21 15:56:02]

this is confusing when used in the child class. Rename it to animating_fade()

+
+  bool currently_scrolling() const { return currently_scrolling_; }
+
  private:
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.