Only block container children support pagination struts.

Source/core/layout/LayoutBlockFlow.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 763 matching lines @@
         // line, and we don't want to move all that, since it has already been established that it
         // fits nicely where it is.
         LayoutUnit lineHeight = lineBox.lineBottomWithLeading() - lineBox.lineTopWithLeading();
         LayoutUnit totalLogicalHeight = lineHeight + std::max<LayoutUnit>(0, lineLogicalOffset);
         LayoutUnit pageLogicalHeightAtNewOffset = block.pageLogicalHeightForOffset(lineLogicalOffset + remainingLogicalHeight);
         // It's rather pointless to break before the block if the current line isn't going to
         // fit in the same column or page, so check that as well.
         if (totalLogicalHeight < pageLogicalHeightAtNewOffset)
             wantsStrutOnBlock = true;
     }
-    // If we want to break before the block, one final check is needed, since some block object
-    // types cannot handle struts.
-    return wantsStrutOnBlock && !block.isOutOfFlowPositioned() && !block.isTableCell();
+    // The block needs to be contained by a LayoutBlockFlow (and not by e.g. a flexbox or a table
+    // (which would be the case for table cell or table caption)). The reason for this limitation is
+    // simply that LayoutBlockFlow child layout code is the only place where we pick up the struts
+    // and handle them. We handle floats and regular in-flow children, and that's all. We could
+    // handle this in other layout modes as well (and even for out-of-flow children), but currently
+    // we don't.
+    if (!wantsStrutOnBlock || block.isOutOfFlowPositioned())
+        return false;
+    LayoutBlock* containingBlock = block.containingBlock();
+    return containingBlock && containingBlock->isLayoutBlockFlow();
 }
 
 void LayoutBlockFlow::adjustLinePositionForPagination(RootInlineBox& lineBox, LayoutUnit& delta)
 {
     // TODO(mstensho): Pay attention to line overflow. It should be painted in the same column as
     // the rest of the line, possibly overflowing the column. We currently only allow overflow above
     // the first column. We clip at all other column boundaries, and that's how it has to be for
     // now. The paint we have to do when a column has overflow has to be special. We need to exclude
     // content that paints in a previous column (and content that paints in the following column).
     //
@@ skipping 2280 matching lines @@
     FrameView* frameView = document().view();
     LayoutUnit top = (style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height();
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (size().height() < visibleHeight)
         top += (visibleHeight - size().height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }
 
 } // namespace blink