Add metric to know how user use scrollbar

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

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index 983b32826d2e339f7db46b4df500c98be43a6ec5..3e7fee1f58d1f54af0fb1b20a1a59da0da20581c 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -518,6 +518,8 @@ class CORE_EXPORT FrameView final
            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