Respect break-inside:avoid on table rows

third_party/WebKit/Source/core/layout/LayoutTableCell.cpp

Index: third_party/WebKit/Source/core/layout/LayoutTableCell.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableCell.cpp b/third_party/WebKit/Source/core/layout/LayoutTableCell.cpp
index 0fc9192c6c566f8e62a348534055b936b1872ee2..f1a72034116bd257f8b8c6a5a79c35cb5f2ddb81 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableCell.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutTableCell.cpp
@@ -999,4 +999,15 @@ bool LayoutTableCell::backgroundIsKnownToBeOpaqueInRect(const LayoutRect& localR
     return LayoutBlockFlow::backgroundIsKnownToBeOpaqueInRect(localRect);
 }
 
+LayoutUnit LayoutTableCell::calculatePaginationStrutToFitContent(LayoutUnit offset, LayoutUnit strutToNextPage, LayoutUnit contentLogicalHeight) const
+{
+    // If break-inside:avoid/forbid is set on a cell we should avoid setting a strut on lines unless the cell is taller than the page,
+    // in which case we've no choice but to allow it. This special-casing is needed because cells don't propagate struts like normal
+    // layout blocks - the struts are managed directly by the section when it lays out rows and cells.
+    LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(offset);
+    if (toLayoutBox(parent())->getPaginationBreakability() != AllowAnyBreaks && table()->vBorderSpacing() + logicalHeight() + contentLogicalHeight < pageLogicalHeight)

[mstensho (USE GERRIT), 2016/04/04 21:05:39]

I still think this looks strange. We have decided that we need to break here
(e.g. between two lines inside a table cell), but we just nuke the strut, and
brutally slice content across column boundaries. This looks like a hack to me. I
wonder if the problem is in LayoutTableSection::layoutRows(). I prefer if we
just leave the strut as it is here, and instead adjust the row heights correctly
in LayoutTableSection::layoutRows(). When paginationStrutForRow() gives us
something there, we should lay out all affected cells over again, and pay
attention if their heights change. Cell heights will typically shrink, since
there'll typically be fewer pagination struts inside. This height decrease needs
to be propagated to all consecutive rows.

This code here also assumes that logicalHeight() is flush with the bottom for
the piece of content that we're supposed to break after, and it doesn't seem
like that's always the case. Which seems to be the reason why this fails:

<div style="columns:2; column-fill:auto; height:5em; line-height:2em;">
    first column<br>
    <table cellpadding="1" cellspacing="0">
        <tr style="break-inside: avoid;">
            <td>second column<br>second column</td>
        </tr>
    </table>
</div>

I'd also like to point out that fragmentation inside tables is quite broken, in
fact, because we don't always lay out the objects at their correct location; see
crbug.com/534751 - a source of weird and broken layout.

+        return LayoutUnit();
+    return LayoutBlockFlow::calculatePaginationStrutToFitContent(offset, strutToNextPage, contentLogicalHeight);
+}
+
 } // namespace blink