[LayoutNG] Auto top/bottom margins may resolve to negative values.

The spec doesn't say that auto margin-top or margin-bottom need to resolve to something non-negative, so just allow negative values as well. They don't cause over-constrainedness. Also, when distributing the space to margin-top and margin-bottom, make sure that everything gets distributed. Set margin-top to the half, and set margin-bottom to total space MINUS margin-top. Just dividing both by two might cause us to lose a tiny fraction of the total, due to rounding. Bug: 888270 Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng Change-Id: Ia10577851e60707a0e2d67857a1c43a12e28b9d2 Reviewed-on: https://chromium-review.googlesource.com/c/1269855 Commit-Queue: Morten Stenshorne <[email protected]> Reviewed-by: Emil A Eklund <[email protected]> Reviewed-by: Christian Biesinger <[email protected]> Reviewed-by: Aleks Totic <[email protected]> Cr-Commit-Position: refs/heads/master@{#598052}
web-platform-tests · Oct 9, 2018 · 600cd35 · 600cd35
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diff --git a/css/CSS2/positioning/absolute-non-replaced-height-013.html b/css/CSS2/positioning/absolute-non-replaced-height-013.html
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+<!DOCTYPE html>
+<title>Auto margin-top and margin-bottom, non-auto everything else</title>
+<link rel="author" title="Morten Stenshorne" href="[email protected]">
+<link rel="help" href="https://www.w3.org/TR/CSS22/visudet.html#abs-non-replaced-height">
+<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="position:relative; width:100px; height:100px; background:red;">
+  <div style="position:absolute; top:50%; bottom:50%; width:100px; height:100px; margin:auto; background:green;"></div>
+</div>