Avoid fragmentainer overflow from children of monolithic content.

Checking if the border box of a monolithic element can fit in the current fragmentainer isn't enough. Children may overflow its border box, and it's this size that we need to consider when determining whether a monolithic element can fit in the current fragmentainer, or if we have to push it to the next one. Had to add a work-around to fast/multicol/vertical-lr/balancing/balance-unbreakable.html to prevent the (monolithic) IMG element (with alt text) in the test from messing up. The broken image symbol got incorrectly aligned and therefore incorrectly contributed to overflow. Reported crbug.com/1178743 for this. Use a real image as a work-around. My first attempt was to switch the IMG to writing-mode:horizontal-tb, but that messes up legacy column balancing. Oh well... Bug: 1178742 Change-Id: Iffbe55d53f32003ae58b574bb6a38745bb92d42e
web-platform-tests · Feb 23, 2021 · fccdb77 · fccdb77
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diff --git a/css/css-break/monolithic-with-overflow.html b/css/css-break/monolithic-with-overflow.html
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+<!DOCTYPE html>
+<link rel="author" title="Morten Stenshorne" href="mailto:mstensho@chromium.org">
+<link rel="help" href="https://www.w3.org/TR/css-break-3/#monolithic">
+<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
+<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
+<div style="columns:2; column-gap:0; column-fill:auto; width:100px; height:100px; background:red;">
+  <div style="height:100px; background:green;"></div>
+  <div style="contain:size; height:0;">
+    <div style="height:100px; background:green;"></div>
+  </div>
+</div>