Add metric to know how user use scrollbar

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

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index dff9ec6cdf05317ec33675b3d62167066f24030e..bb2e69e8ac8d45d6edaf3f7d3d0b4b54d24c73d0 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -271,6 +271,7 @@ void FrameView::reset() {
   m_viewportConstrainedObjects.reset();
   m_layoutSubtreeRootList.clear();
   m_orthogonalWritingModeRootList.clear();
+  m_sentScrollbarUseUMA.reset();
 }
 
 // Call function for each non-throttled frame view in pre tree order.
@@ -3757,6 +3758,13 @@ void FrameView::setScrollbarModes(ScrollbarMode horizontalMode,
                            userInputScrollable(VerticalScrollbar));
 }
 
+bool FrameView::shouldSendScrollbarUseUMA(int part) {
+  if (m_sentScrollbarUseUMA[part])
+    return false;
+  m_sentScrollbarUseUMA[part] = true;
+  return true;
+}
+
 IntSize FrameView::visibleContentSize(
     IncludeScrollbarsInRect scrollbarInclusion) const {
   return scrollbarInclusion == ExcludeScrollbars