Add initial UMA metrics for ScrollAnchoring

third_party/WebKit/Source/core/layout/ScrollAnchor.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/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 {
 
 using Corner = ScrollAnchor::Corner;
 
 ScrollAnchor::ScrollAnchor(ScrollableArea* scroller)
     : m_scroller(scroller)
     , m_anchorObject(nullptr)
     , m_corner(Corner::TopLeft)
 {
@@ skipping 135 matching lines @@
 void ScrollAnchor::restore()
 {
     if (!m_anchorObject)
         return;
 
     LayoutSize adjustment = computeRelativeOffset(m_anchorObject, m_scroller, m_corner) - m_savedRelativeOffset;
     if (!adjustment.isZero()) {
         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);
+        }
     }
 }
 
 void ScrollAnchor::clear()
 {
     LayoutObject* anchorObject = m_anchorObject;
     m_anchorObject = nullptr;
 
     if (anchorObject)
         anchorObject->maybeClearIsScrollAnchorObject();
 }
 
 } // namespace blink