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

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

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 1399 matching lines @@
         MutableForPainting(const LayoutObject& layoutObject) : m_layoutObject(const_cast<LayoutObject&>(layoutObject)) { }
 
         LayoutObject& m_layoutObject;
     };
     MutableForPainting getMutableForPainting() const { return MutableForPainting(*this); }
 
     void setIsScrollAnchorObject() { m_bitfields.setIsScrollAnchorObject(true); }
     // 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;
     IntSize scrollAdjustmentForPaintInvalidation(const LayoutBoxModelObject& paintInvalidationContainer) const;
 
     bool previousBackgroundObscured() const { return m_bitfields.previousBackgroundObscured(); }
     void setPreviousBackgroundObscured(bool b) { m_bitfields.setPreviousBackgroundObscured(b); }
 
 protected:
     enum LayoutObjectType {
@@ skipping 301 matching lines @@
             , m_isInsideFlowThread(false)
             , m_subtreeChangeListenerRegistered(false)
             , m_notifiedOfSubtreeChange(false)
             , m_consumesSubtreeChangeNotification(false)
             , m_childrenInline(false)
             , m_containsInlineWithOutlineAndContinuation(false)
             , m_alwaysCreateLineBoxesForLayoutInline(false)
             , m_previousBackgroundObscured(false)
             , m_isBackgroundAttachmentFixedObject(false)
             , m_isScrollAnchorObject(false)
+            , m_hasLayoutAffectingStyleChanged(false)
             , m_hasBoxDecorationBackground(false)
             , m_positionedState(IsStaticallyPositioned)
             , m_selectionState(SelectionNone)
             , m_backgroundObscurationState(BackgroundObscurationStatusInvalid)
             , m_fullPaintInvalidationReason(PaintInvalidationNone)
         {
         }
 
         // 32 bits have been used in the first word, and 18 in the second.
 
@@ skipping 118 matching lines @@
 
         // from LayoutInline
         ADD_BOOLEAN_BITFIELD(alwaysCreateLineBoxesForLayoutInline, AlwaysCreateLineBoxesForLayoutInline);
 
         // Background obscuration status of the previous frame.
         ADD_BOOLEAN_BITFIELD(previousBackgroundObscured, PreviousBackgroundObscured);
 
         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:
         // This is the cached 'position' value of this object
         // (see ComputedStyle::position).
         unsigned m_positionedState : 2; // PositionedState
         unsigned m_selectionState : 3; // SelectionState
         // Mutable for getter which lazily update this field.
         mutable unsigned m_backgroundObscurationState : 2; // BackgroundObscurationState
         unsigned m_fullPaintInvalidationReason : 5; // PaintInvalidationReason
@@ skipping 142 matching lines @@
     setSelfNeedsLayout(false);
     setPosChildNeedsLayout(false);
     setNeedsSimplifiedNormalFlowLayout(false);
     setNormalChildNeedsLayout(false);
     setNeedsPositionedMovementLayout(false);
     setAncestorLineBoxDirty(false);
 
 #if ENABLE(ASSERT)
     checkBlockPositionedObjectsNeedLayout();
 #endif
+
+    setHasLayoutAffectingStyleChanged(false);
 }
 
 inline void LayoutObject::setChildNeedsLayout(MarkingBehavior markParents, SubtreeLayoutScope* layouter)
 {
     ASSERT(!isSetNeedsLayoutForbidden());
     bool alreadyNeededLayout = normalChildNeedsLayout();
     setNormalChildNeedsLayout(true);
     // FIXME: Replace MarkOnlyThis with the SubtreeLayoutScope code path and remove the MarkingBehavior argument entirely.
     if (!alreadyNeededLayout && markParents == MarkContainerChain && (!layouter || layouter->root() != this))
         markContainerChainForLayout(!layouter, layouter);
@@ skipping 106 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h