Add metric to know how user use scrollbar

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 
 #include "core/frame/Settings.h"
+#include "core/frame/UseCounter.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutScrollbar.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/paint/ObjectPaintInvalidator.h"
 #include "core/paint/PaintInvalidator.h"
 #include "core/paint/PaintLayer.h"
 #include "platform/graphics/GraphicsLayer.h"
 
 namespace blink {
@@ skipping 179 matching lines @@
   fullBounds.unite(m_verticalScrollbarPreviousVisualRect);
   fullBounds.unite(m_scrollCornerAndResizerPreviousVisualRect);
   return fullBounds;
 }
 
 void PaintInvalidationCapableScrollableArea::
     scrollControlWasSetNeedsPaintInvalidation() {
   layoutBox()->setMayNeedPaintInvalidation();
 }
 
+void PaintInvalidationCapableScrollableArea::didScrollWithScrollbar(
+    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(layoutBox()->document(), scrollbarUseUMA);
+}
+
 }  // namespace blink