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

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

 // 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.
 
 #ifndef ScrollAnchor_h
 #define ScrollAnchor_h
 
 #include "core/CoreExport.h"
 #include "platform/geometry/LayoutPoint.h"
 #include "platform/heap/Handle.h"
@@ skipping 14 matching lines @@
 
     // The scroller that is scrolled to componsate for layout movements. Note
     // that the scroller can only be initialized once.
     void setScroller(ScrollableArea*);
 
     // Returns true if the underlying scroller is set.
     bool hasScroller() const { return m_scroller; }
 
     // The LayoutObject we are currently anchored to. Lazily computed during
     // save() and cached until the next call to clear().
-    LayoutObject* anchorObject() const { return m_current.m_anchorObject; }
+    LayoutObject* anchorObject() const { return m_anchorObject; }
 
     // Indicates that the next save() should compute a new anchor. (In certain
     // cases the previous anchor will be reused; see comments in restore.)
     void clear();
 
     // Records the anchor's location in relation to the scroller. Should be
     // called when the scroller is about to be laid out.
     void save();
 
     // Scrolls to compensate for any change in the anchor's relative location
     // since the most recent call to save(). Should be called immediately after
     // the scroller has been laid out.
     void restore();
 
     enum class Corner {
         TopLeft = 0,
         TopRight,
     };
     // Which corner of the anchor object we are currently anchored to.
     // Only meaningful if anchorObject() is non-null.
-    Corner corner() const { return m_current.m_corner; }
+    Corner corner() const { return m_corner; }
 
     // Checks if we hold any references to the specified object.
     bool refersTo(const LayoutObject*) const;
 
     // Notifies us that an object will be removed from the layout tree.
     void notifyRemoved(LayoutObject*);
 
     DEFINE_INLINE_TRACE() { visitor->trace(m_scroller); }
 
 private:
     void findAnchor();
+    bool computeScrollAnchorDisablingStyleChanged();
 
     enum WalkStatus {
         Skip = 0,
         Constrain,
         Continue,
         Return
     };
     struct ExamineResult {
         ExamineResult(WalkStatus s)
             : status(s)
             , viable(false)
             , corner(Corner::TopLeft) {}
 
         ExamineResult(WalkStatus s, Corner c)
             : status(s)
             , viable(true)
             , corner(c) {}
 
         WalkStatus status;
         bool viable;
         Corner corner;
     };
     ExamineResult examine(const LayoutObject*) const;
 
-    struct AnchorPoint {
-        AnchorPoint()
-            : m_anchorObject(nullptr)
-            , m_corner(Corner::TopLeft) {}
-
-        AnchorPoint(LayoutObject* anchorObject, Corner corner)
-            : m_anchorObject(anchorObject)
-            , m_corner(corner) {}
-
-        explicit operator bool() const { return m_anchorObject; }
-
-        void clear();
-
-        // The LayoutObject we should anchor to.
-        LayoutObject* m_anchorObject;
-
-        // Which corner of m_anchorObject's bounding box to anchor to.
-        Corner m_corner;
-
-        // Location of m_layoutObject relative to scroller at time of save().
-        LayoutPoint m_savedRelativeOffset;
-    };
-    IntSize computeAdjustment(const AnchorPoint&) const;
-    void adjust(IntSize);
+    IntSize computeAdjustment() const;
 
     // The scroller that owns and is adjusted by this ScrollAnchor.
     Member<ScrollableArea> m_scroller;
 
-    // The current anchor point. Lazily computed.
-    AnchorPoint m_current;
+    // The LayoutObject we should anchor to.
+    LayoutObject* m_anchorObject;
 
-    // The anchor point that was used for the most recent non-zero adjustment.
-    AnchorPoint m_lastAdjusted;
+    // Which corner of m_anchorObject's bounding box to anchor to.
+    Corner m_corner;
 
-    // The size of the most recent non-zero adjustment.
-    IntSize m_lastAdjustment;
+    // Location of m_layoutObject relative to scroller at time of save().
+    LayoutPoint m_savedRelativeOffset;
 
-    // True iff the last adjustment was the exact opposite of the one before it.
-    // A bounce suggests a circular interaction with a scroll event handler.
-    bool m_hasBounced;
-
-    // Number of adjustments made since the last clear().
-    int m_adjustmentCount;
+    // Whether the anchor node or an ancestor (up to and including the scroller)
+    // has had a scroll-anchor-disabling style changed since the last layout.

[ojan, 2016/08/18 18:39:48]

Nit: Might want to add a bit more to this so people don't have to go to the
bit.ly link to understand. Just something like:
Style changes on the node or one of it's ancestors that can cause the node to
move disable scroll anchoring.

[skobes, 2016/08/18 21:43:42]

Done.

+    // This field is recomputed in save() and used to suppress the adjustment.
+    // See http://bit.ly/sanaclap for more info.
+    bool m_scrollAnchorDisablingStyleChanged;
 };
 
 } // namespace blink
 
 #endif // ScrollAnchor_h