Implement SANACLAP (http://bit.ly/sanaclap).

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index d0d231ec9312fbfbf1a1bd3c54fdb8f852592751..a0e501ef0796e979fec87f7b34074e7583661a0b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -1417,6 +1417,9 @@ public:
     // Clears the IsScrollAnchorObject bit, unless any ScrollAnchor still refers to us.
     void maybeClearIsScrollAnchorObject();
 
+    bool hasLayoutAffectingStyleChanged() { return m_bitfields.hasLayoutAffectingStyleChanged(); }

[ojan, 2016/08/16 23:54:32]

<bikeshed>This name might be too general. It's not clear without reading all the
code involved what the difference is from the needsLayout bits. Maybe we should
just call this something very specific like scrollAnchorDisablingStyleChanged?

[skobes, 2016/08/17 18:50:32]

Done.

+    void setHasLayoutAffectingStyleChanged(bool changed) { m_bitfields.setHasLayoutAffectingStyleChanged(changed); }
+
     void clearChildNeedsOverflowRecalcAfterStyleChange() { m_bitfields.setChildNeedsOverflowRecalcAfterStyleChange(false); }
 
     bool compositedScrollsWithRespectTo(const LayoutBoxModelObject& paintInvalidationContainer) const;
@@ -1738,6 +1741,7 @@ private:
             , m_previousBackgroundObscured(false)
             , m_isBackgroundAttachmentFixedObject(false)
             , m_isScrollAnchorObject(false)
+            , m_hasLayoutAffectingStyleChanged(false)
             , m_hasBoxDecorationBackground(false)
             , m_positionedState(IsStaticallyPositioned)
             , m_selectionState(SelectionNone)
@@ -1876,6 +1880,11 @@ private:
         ADD_BOOLEAN_BITFIELD(isBackgroundAttachmentFixedObject, IsBackgroundAttachmentFixedObject);
         ADD_BOOLEAN_BITFIELD(isScrollAnchorObject, IsScrollAnchorObject);
 
+        // This bit is used for scroll anchoring. It indicates whether this LayoutObject has
+        // changed the value of one or more CSS properties that may affect its position.
+        // See http://bit.ly/sanaclap for more info.
+        ADD_BOOLEAN_BITFIELD(hasLayoutAffectingStyleChanged, HasLayoutAffectingStyleChanged);
+
         ADD_BOOLEAN_BITFIELD(hasBoxDecorationBackground, HasBoxDecorationBackground);
 
     private:
@@ -2038,6 +2047,8 @@ inline void LayoutObject::clearNeedsLayout()
 #if ENABLE(ASSERT)
     checkBlockPositionedObjectsNeedLayout();
 #endif
+
+    setHasLayoutAffectingStyleChanged(false);
 }
 
 inline void LayoutObject::setChildNeedsLayout(MarkingBehavior markParents, SubtreeLayoutScope* layouter)