Show Overlay Scrollbar when GestureScrollUpdate

cc/input/scrollbar_animation_controller.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 47 matching lines @@
       base::TimeDelta fade_out_resize_delay,
       base::TimeDelta fade_out_duration,
       base::TimeDelta thinning_duration);
 
   ~ScrollbarAnimationController();
 
   bool ScrollbarsHidden() const;
 
   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();
   void DidMouseUp();
   void DidMouseLeave();
   void DidMouseMoveNear(ScrollbarOrientation, float);
 
   bool MouseIsOverScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearAnyScrollbar() const;
@@ skipping 68 matching lines @@
       vertical_controller_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       horizontal_controller_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_