Don't eat margins when column height isn't yet known.

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
  * version 2 of the License, or (at your option) any later version.
@@ skipping 394 matching lines @@
     LayoutBlock* continuationBefore(LayoutObject* beforeChild);
     LayoutBlockFlow* containingColumnsBlock(bool allowAnonymousColumnBlock = true);
     LayoutBlockFlow* columnsBlockForSpanningElement(LayoutObject* newChild);
 
     // End helper functions and structs used by layoutBlockChildren.
 
     void removeFromGlobalMaps();
     bool widthAvailableToChildrenHasChanged();
 
 protected:
+    bool isPageLogicalHeightKnown(LayoutUnit logicalOffset) const { return pageLogicalHeightForOffset(logicalOffset); }
+
     // Returns the logicalOffset at the top of the next page. If the offset passed in is already at the top of the current page,
     // then nextPageLogicalTop with ExcludePageBoundary will still move to the top of the next page. nextPageLogicalTop with
     // IncludePageBoundary set will not.
     //
     // For a page height of 800px, the first rule will return 800 if the value passed in is 0. The second rule will simply return 0.
     enum PageBoundaryRule { ExcludePageBoundary, IncludePageBoundary };
     LayoutUnit nextPageLogicalTop(LayoutUnit logicalOffset, PageBoundaryRule = ExcludePageBoundary) const;
 
     bool createsNewFormattingContext() const;
 
@@ skipping 39 matching lines @@
     // FIXME: This is temporary as we move code that accesses block flow
     // member variables out of LayoutBlock and into LayoutBlockFlow.
     friend class LayoutBlockFlow;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutBlock, isLayoutBlock());
 
 } // namespace blink
 
 #endif // LayoutBlock_h