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 8dca0e8f9700cd8ca2a3826cac3351acb2f3da67..7350756eb8c641e8859d2d9ac587878315e71ebd 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -55,6 +55,7 @@
 #include "core/frame/RemoteFrame.h"
 #include "core/frame/RemoteFrameView.h"
 #include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
 #include "core/frame/VisualViewport.h"
 #include "core/html/HTMLFrameElement.h"
 #include "core/html/HTMLPlugInElement.h"
@@ -3756,6 +3757,39 @@ void FrameView::setScrollbarModes(ScrollbarMode horizontalMode,
                            userInputScrollable(VerticalScrollbar));
 }
 
+void FrameView::sendScrollbarUseUMA(ScrollbarPart part,
+                                    ScrollbarOrientation orientation) {
+  UseCounter::Feature scrollbarUseUMA;
+  switch (part) {
+    case BackButtonStartPart:
+    case ForwardButtonStartPart:
+    case BackButtonEndPart:
+    case ForwardButtonEndPart:
+      scrollbarUseUMA =
+          (orientation == VerticalScrollbar
+               ? UseCounter::ScrollbarUseVerticalScrollbarButton
+               : UseCounter::ScrollbarUseHorizontalScrollbarButton);
+      break;
+    case ThumbPart:
+      scrollbarUseUMA =
+          (orientation == VerticalScrollbar
+               ? UseCounter::ScrollbarUseVerticalScrollbarThumb
+               : UseCounter::ScrollbarUseHorizontalScrollbarThumb);
+      break;
+    case BackTrackPart:
+    case ForwardTrackPart:
+      scrollbarUseUMA =
+          (orientation == VerticalScrollbar
+               ? UseCounter::ScrollbarUseVerticalScrollbarTrack
+               : UseCounter::ScrollbarUseHorizontalScrollbarTrack);
+      break;
+    default:
+      return;
+  }
+
+  UseCounter::count(&frame(), scrollbarUseUMA);
+}
+
 IntSize FrameView::visibleContentSize(
     IncludeScrollbarsInRect scrollbarInclusion) const {
   return scrollbarInclusion == ExcludeScrollbars