Add metric to know how user use scrollbar

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

Index: third_party/WebKit/Source/core/frame/UseCounter.h
diff --git a/third_party/WebKit/Source/core/frame/UseCounter.h b/third_party/WebKit/Source/core/frame/UseCounter.h
index 2fa053d0b43cabe3056bcca19aa3a45ebdfe35fc..cfecd425422c18d7cb60d4499399bee5fd96c6c2 100644
--- a/third_party/WebKit/Source/core/frame/UseCounter.h
+++ b/third_party/WebKit/Source/core/frame/UseCounter.h
@@ -1439,6 +1439,12 @@ class CORE_EXPORT UseCounter {
     DocumentCompleteURLHTTPContainingLessThan = 1769,
     DocumentCompleteURLHTTPContainingNewlineAndLessThan = 1770,
     DocumentCompleteURLNonHTTPContainingNewlineOrLessThan = 1771,
+    ScrollbarUseVerticalScrollbarButton = 1772,
+    ScrollbarUseVerticalScrollbarThumb = 1773,
+    ScrollbarUseVerticalScrollbarTrack = 1774,
+    ScrollbarUseHorizontalScrollbarButton = 1775,
+    ScrollbarUseHorizontalScrollbarThumb = 1776,
+    ScrollbarUseHorizontalScrollbarTrack = 1777,
 
     // Add new features immediately above this line. Don't change assigned
     // numbers of any item, and don't reuse removed slots.