Add metric to know how user use scrollbar

third_party/WebKit/Source/platform/scroll/Scrollbar.h

Index: third_party/WebKit/Source/platform/scroll/Scrollbar.h
diff --git a/third_party/WebKit/Source/platform/scroll/Scrollbar.h b/third_party/WebKit/Source/platform/scroll/Scrollbar.h
index a9cf98a131a2324eda0fa4c463733d68ebab51a1..dda90c03e278498a083417751fd09ea1044fa4dc 100644
--- a/third_party/WebKit/Source/platform/scroll/Scrollbar.h
+++ b/third_party/WebKit/Source/platform/scroll/Scrollbar.h
@@ -44,6 +44,17 @@ class ScrollableArea;
 class ScrollbarTheme;
 class WebGestureEvent;
 
+enum ScrollbarUseUMA {
+  IgnorePart = 0,
+  VerticalScrollbarButton,
+  VerticalScrollbarThumb,
+  VerticalScrollbarTrack,
+  HorizontalScrollbarButton,
+  HorizontalScrollbarThumb,
+  HorizontalScrollbarTrack,
+  ScrollbarUseUMAMax
+};
+
 class PLATFORM_EXPORT Scrollbar : public Widget,
                                   public ScrollbarThemeClient,
                                   public DisplayItemClient {
@@ -252,6 +263,8 @@ class PLATFORM_EXPORT Scrollbar : public Widget,
   float scrollableAreaTargetPos() const;
   bool thumbWillBeUnderMouse() const;
 
+  void sendScrollbarUseUMA(ScrollbarPart);
+
   int m_themeScrollbarThickness;
   bool m_trackNeedsRepaint;
   bool m_thumbNeedsRepaint;