Revert of Show Overlay Scrollbar when GestureScrollUpdate

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 262354386331b306337d8587da29aadff14ffb26..02f8e97d2cbc049b1691203b47583a481dab10ec 100644
--- a/cc/input/scrollbar_animation_controller.h
+++ b/cc/input/scrollbar_animation_controller.h
@@ -65,19 +65,8 @@ class CC_EXPORT ScrollbarAnimationController {
 
   bool Animate(base::TimeTicks now);
 
-  // WillUpdateScroll expects to be called even if the scroll position won't
-  // change as a result of the scroll. Only effect Aura Overlay Scrollbar.
-  void WillUpdateScroll();
-
-  // DidScrollUpdate expects to be called only if the scroll position change.
-  // Effect both Android and Aura Overlay Scrollbar.
-  void DidScrollUpdate();
-
-  // DidResize expects to be called when clip layer size changed or scroll layer
-  // size changed.
-  void DidResize();
-
   void DidScrollBegin();
+  void DidScrollUpdate(bool on_resize);
   void DidScrollEnd();
 
   void DidMouseDown();
@@ -154,7 +143,6 @@ class CC_EXPORT ScrollbarAnimationController {
   float opacity_;
   base::TimeDelta fade_out_duration_;
 
-  const bool show_scrollbars_on_scroll_gesture_;
   const bool need_thinning_animation_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       vertical_controller_;