Content that starts before the first fragmentainer should stay where it is.

third_party/WebKit/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 962 matching lines @@
             setPaginationStrutPropagatedFromChild(strut);
         } else {
             delta += paginationStrut;
             lineBox.setPaginationStrut(paginationStrut);
             lineBox.setIsFirstAfterPageBreak(true);
         }
         paginatedContentWasLaidOut(newLogicalOffset + lineHeight);
         return;
     }
 
+    LayoutUnit strutToPropagate;
     if (remainingLogicalHeight == pageLogicalHeight) {
         // We're at the very top of a page or column.
         if (lineBox != firstRootBox())
             lineBox.setIsFirstAfterPageBreak(true);
         // If this is the first line in the block, and the block has a top border, padding, or (in
         // case it's a float) margin, we may want to set a strut on the block, so that everything
         // ends up in the next column or page. Setting a strut on the block is also important when
         // it comes to satisfying orphan requirements.
-        if (shouldSetStrutOnBlock(*this, lineBox, logicalOffset, lineIndex, pageLogicalHeight)) {
-            LayoutUnit strut = logicalOffset + marginBeforeIfFloating();
-            setPaginationStrutPropagatedFromChild(strut);
-        }
+        if (shouldSetStrutOnBlock(*this, lineBox, logicalOffset, lineIndex, pageLogicalHeight))
+            strutToPropagate = logicalOffset + marginBeforeIfFloating();
     } else if (lineBox == firstRootBox() && allowsPaginationStrut()) {
         // This is the first line in the block. The block may still start in the previous column or
         // page, and if that's the case, attempt to pull it over to where this line is, so that we
         // don't split the top border, padding, or (in case it's a float) margin.
         LayoutUnit totalLogicalOffset = logicalOffset + marginBeforeIfFloating();
         LayoutUnit strut = remainingLogicalHeight + totalLogicalOffset - pageLogicalHeight;
         if (strut > 0) {
             // The block starts in a previous column or page. Set a strut on the block if there's
             // room for the top border, padding and (if it's a float) margin and the line in one
             // column or page.
             if (totalLogicalOffset + lineHeight <= pageLogicalHeight)
-                setPaginationStrutPropagatedFromChild(strut);
+                strutToPropagate = strut;
         }
     }
 
+    // If we found that some preceding content (lines, border and padding) belongs together with
+    // this line, we should pull the entire block with us to the fragmentainer we're currently
+    // in. We need to avoid this when the block precedes the first fragmentainer, though. We
+    // shouldn't fragment content there, but rather let it appear in the overflow area before the
+    // first fragmentainer.
+    if (strutToPropagate && offsetFromLogicalTopOfFirstPage() > LayoutUnit())
+        setPaginationStrutPropagatedFromChild(strutToPropagate);
+
     paginatedContentWasLaidOut(logicalOffset + lineHeight);
 }
 
 LayoutUnit LayoutBlockFlow::adjustForUnsplittableChild(LayoutBox& child, LayoutUnit logicalOffset) const
 {
     if (child.getPaginationBreakability() == AllowAnyBreaks)
         return logicalOffset;
     LayoutUnit childLogicalHeight = logicalHeightForChild(child);
     // Floats' margins do not collapse with page or column boundaries.
     if (child.isFloating())
@@ skipping 2753 matching lines @@
 
     return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(PaintInvalidationReason invalidationReason) const
 {
     BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(invalidationReason);
 }
 
 } // namespace blink