Behave more normally for content taller than the fragmentainer it's in.

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 757 matching lines @@
     // line and all following lines.
     LayoutRect logicalVisualOverflow = lineBox.logicalVisualOverflowRect(lineBox.lineTop(), lineBox.lineBottom());
     LayoutUnit logicalOffset = std::min(lineBox.lineTopWithLeading(), logicalVisualOverflow.y());
     LayoutUnit logicalBottom = std::max(lineBox.lineBottomWithLeading(), logicalVisualOverflow.maxY());
     LayoutUnit lineHeight = logicalBottom - logicalOffset;
     updateMinimumPageHeight(logicalOffset, calculateMinimumPageHeight(styleRef(), &lineBox, logicalOffset, logicalBottom));
     logicalOffset += delta;
     lineBox.setPaginationStrut(0);
     lineBox.setIsFirstAfterPageBreak(false);
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
-    bool hasUniformPageLogicalHeight = !flowThread || flowThread->columnSetsHaveUniformLogicalHeight();
-    // If lineHeight is greater than pageLogicalHeight, but logicalVisualOverflow.height() still fits, we are
-    // still going to add a strut, so that the visible overflow fits on a single page.
-    if (!pageLogicalHeight || (hasUniformPageLogicalHeight && logicalVisualOverflow.height() > pageLogicalHeight)) {
-        // FIXME: In case the line aligns with the top of the page (or it's slightly shifted downwards) it will not be marked as the first line in the page.
-        // From here, the fix is not straightforward because it's not easy to always determine when the current line is the first in the page.
+    if (!pageLogicalHeight)
         return;
-    }
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);
 
     int lineIndex = lineCount(&lineBox);
     if (remainingLogicalHeight < lineHeight || (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex)) {
         if (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex) {
             clearShouldBreakAtLineToAvoidWidow();
             setDidBreakAtLineToAvoidWidow();
         }
         if (lineHeight > pageLogicalHeight) {
             // Split the top margin in order to avoid splitting the visible part of the line.
             remainingLogicalHeight -= std::min(lineHeight - pageLogicalHeight, std::max<LayoutUnit>(0, logicalVisualOverflow.y() - lineBox.lineTopWithLeading()));
         }
         LayoutUnit totalLogicalHeight = lineHeight + std::max<LayoutUnit>(0, logicalOffset);
-        LayoutUnit pageLogicalHeightAtNewOffset = hasUniformPageLogicalHeight ? pageLogicalHeight : pageLogicalHeightForOffset(logicalOffset + remainingLogicalHeight);
+        LayoutUnit pageLogicalHeightAtNewOffset = pageLogicalHeightForOffset(logicalOffset + remainingLogicalHeight);
         setPageBreak(logicalOffset, lineHeight - remainingLogicalHeight);
         if (((lineBox == firstRootBox() && totalLogicalHeight < pageLogicalHeightAtNewOffset) || (!style()->hasAutoOrphans() && style()->orphans() >= lineIndex))
             && !isOutOfFlowPositioned() && !isTableCell()) {
             setPaginationStrut(remainingLogicalHeight + std::max<LayoutUnit>(0, logicalOffset));
         } else {
             delta += remainingLogicalHeight;
             lineBox.setPaginationStrut(remainingLogicalHeight);
             lineBox.setIsFirstAfterPageBreak(true);
         }
     } else if (remainingLogicalHeight == pageLogicalHeight) {
         // We're at the very top of a page or column.
         if (lineBox != firstRootBox())
             lineBox.setIsFirstAfterPageBreak(true);
         if (lineBox != firstRootBox() || offsetFromLogicalTopOfFirstPage())
             setPageBreak(logicalOffset, lineHeight);
     }
 }
 
 LayoutUnit LayoutBlockFlow::adjustForUnsplittableChild(LayoutBox& child, LayoutUnit logicalOffset, bool includeMargins)
 {
     bool checkColumnBreaks = flowThreadContainingBlock();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight();
     bool isUnsplittable = child.isUnsplittableForPagination() || (checkColumnBreaks && child.style()->columnBreakInside() == PBAVOID)
         || (checkPageBreaks && child.style()->pageBreakInside() == PBAVOID);
     if (!isUnsplittable)
         return logicalOffset;
     LayoutUnit childLogicalHeight = logicalHeightForChild(child) + (includeMargins ? marginBeforeForChild(child) + marginAfterForChild(child) : LayoutUnit());
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     updateMinimumPageHeight(logicalOffset, childLogicalHeight);
-    if (!pageLogicalHeight || childLogicalHeight > pageLogicalHeight)
+    if (!pageLogicalHeight)
         return logicalOffset;
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);
     if (remainingLogicalHeight < childLogicalHeight)
         return logicalOffset + remainingLogicalHeight;
     return logicalOffset;
 }
 
 void LayoutBlockFlow::rebuildFloatsFromIntruding()
 {
     if (m_floatingObjects)
@@ skipping 2238 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