Add initial UMA metrics for ScrollAnchoring

third_party/WebKit/Source/core/layout/ScrollAnchor.cpp

Index: third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
diff --git a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
index ba2558be4ea525a692f070152ea8065f091c6b32..76e912ee065e48932c61979ca8d91c33f6124113 100644
--- a/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
+++ b/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
@@ -5,9 +5,11 @@
 #include "core/layout/ScrollAnchor.h"
 
 #include "core/frame/FrameView.h"
+#include "core/frame/UseCounter.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/line/InlineTextBox.h"
 #include "core/paint/PaintLayerScrollableArea.h"
+#include "platform/Histogram.h"
 
 namespace blink {
 
@@ -163,6 +165,16 @@ void ScrollAnchor::restore()
         m_scroller->setScrollPosition(
             m_scroller->scrollPositionDouble() + DoubleSize(adjustment),
             AnchoringScroll);
+        // Update UMA metric.
+        DEFINE_STATIC_LOCAL(EnumerationHistogram, adjustedOffsetHistogram,
+            ("Layout.ScrollAnchor.AdjustedScrollOffset", 2));
+        adjustedOffsetHistogram.count(1);
+        if (m_scroller->isFrameView()) {

[skobes, 2016/03/24 18:59:11]

You can do scrollerLayoutBox(m_scroller)->document() and avoid this branching.

[ymalik, 2016/03/25 19:38:07]

Done.

+            UseCounter::count(toFrameView(m_scroller)->layoutView()->document(), UseCounter::ScrollAnchored);
+        } else {
+            ASSERT(m_scroller->isPaintLayerScrollableArea());
+            UseCounter::count(toPaintLayerScrollableArea(m_scroller)->box().document(), UseCounter::ScrollAnchored);
+        }
     }
 }