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..775cb1bf409e08270d735038d3afa235dfae4b1c 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"
 #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:
@@ -57,16 +58,23 @@ class CC_EXPORT ScrollbarAnimationController {
   virtual void RunAnimationFrame(float progress) = 0;
   virtual const base::TimeDelta& Duration() = 0;
 
-  void StartAnimation();
+  virtual void StartAnimation();
   void StopAnimation();
+
   ScrollbarSet Scrollbars() const;
 
   ScrollbarAnimationControllerClient* client_;
 
   void PostDelayedAnimationTask(bool on_resize);
 
+  base::CancelableClosure* delayed_scrollbar_fade() {
+    return &delayed_scrollbar_fade_;
+  }
+
   int scroll_layer_id() const { return scroll_layer_id_; }
 
+  bool animating() const { return is_animating_; }
+
  private:
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.