Disable anchoring if ancestor changes padding or margin

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 48 matching lines @@
     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 paddingOrBorderChanged() const;
+
     enum WalkStatus {
         Skip = 0,
         Constrain,
         Continue,
         Return
     };
     struct ExamineResult {
         ExamineResult(WalkStatus s)
             : status(s)
             , viable(false)
@@ skipping 46 matching lines @@
 
     // The size of the most recent non-zero adjustment.
     IntSize m_lastAdjustment;
 
     // 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 any of the ancestors had their border/padding modified in the
+    // layout pass that triggered scroll anchoring.
+    bool m_anyAncestorChangedPaddingOrMargin;
 };
 
 } // namespace blink
 
 #endif // ScrollAnchor_h