Margins that start at fragmentainer boundaries should be collapsed away.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple 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
  * License as published by the Free Software Foundation; either
@@ skipping 493 matching lines @@
   // End helper functions and structs used by layoutBlockChildren.
 
   void removeFromGlobalMaps();
   bool widthAvailableToChildrenHasChanged();
 
  protected:
   bool isPageLogicalHeightKnown() const {
     return pageLogicalHeightForOffset(LayoutUnit());
   }
 
-  // Returns the logical offset at the top of the next page, for a given offset.
-  LayoutUnit nextPageLogicalTop(LayoutUnit logicalOffset) const;
-
   // Paginated content inside this block was laid out.
   // |logicalBottomOffsetAfterPagination| is the logical bottom offset of the
   // child content after applying any forced or unforced breaks as needed.
   void paginatedContentWasLaidOut(
       LayoutUnit logicalBottomOffsetAfterPagination);
 
   // Adjust from painting offsets to the local coords of this layoutObject
   void offsetForContents(LayoutPoint&) const;
 
   PositionWithAffinity positionForPointRespectingEditingBoundaries(
@@ skipping 41 matching lines @@
   // TODO(lunalu): Temporary in order to ensure compatibility with existing
   // layout test results.
   virtual void adjustChildDebugRect(LayoutRect&) const {}
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlock, isLayoutBlock());
 
 }  // namespace blink
 
 #endif  // LayoutBlock_h