Add metric to know how user use scrollbar

third_party/WebKit/Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights
    reserved.
 
    This library is free software; you can redistribute it and/or
@@ skipping 500 matching lines @@
 
   void setScrollingModesLock(bool lock = true) {
     m_horizontalScrollbarLock = m_verticalScrollbarLock = lock;
   }
 
   bool canHaveScrollbars() const {
     return horizontalScrollbarMode() != ScrollbarAlwaysOff ||
            verticalScrollbarMode() != ScrollbarAlwaysOff;
   }
 
+  void sendScrollbarUseUMA(ScrollbarPart, ScrollbarOrientation) override;
+
   // The visible content rect has a location that is the scrolled offset of
   // the document. The width and height are the layout viewport width and
   // height. By default the scrollbars themselves are excluded from this
   // rectangle, but an optional boolean argument allows them to be included.
   IntRect visibleContentRect(
       IncludeScrollbarsInRect = ExcludeScrollbars) const override;
   IntSize visibleContentSize(IncludeScrollbarsInRect = ExcludeScrollbars) const;
 
   // Clips the provided rect to the visible content area. For this purpose, we
   // also query the chrome client for any active overrides to the visible area
@@ skipping 692 matching lines @@
                   widget.isFrameView());
 DEFINE_TYPE_CASTS(FrameView,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isFrameView(),
                   scrollableArea.isFrameView());
 
 }  // namespace blink
 
 #endif  // FrameView_h