Add metric to know how user use scrollbar

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

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index 983b32826d2e339f7db46b4df500c98be43a6ec5..03acac3460ce49dc0f522e95a77048193ceedd5b 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -55,6 +55,8 @@
 #include "wtf/HashSet.h"
 #include "wtf/ListHashSet.h"
 #include "wtf/text/WTFString.h"
+
+#include <bitset>
 #include <memory>
 
 namespace blink {
@@ -518,6 +520,8 @@ class CORE_EXPORT FrameView final
            verticalScrollbarMode() != ScrollbarAlwaysOff;
   }
 
+  bool shouldSendScrollbarUseUMA(int part) override;
+
   // The visible content rect has a location that is the scrolled offset of
   // the document. The width and height are the layout viewport width and
   // height. By default the scrollbars themselves are excluded from this
@@ -1102,6 +1106,8 @@ class CORE_EXPORT FrameView final
   bool m_horizontalScrollbarLock;
   bool m_verticalScrollbarLock;
 
+  std::bitset<ScrollbarUseUMAMax> m_sentScrollbarUseUMA;

[bokan, 2017/01/17 17:04:05]

A page will have multiple FrameViews. Put this on FrameHost instead.

+
   ChildrenWidgetSet m_children;
 
   ScrollOffset m_pendingScrollDelta;