[css-flexbox-1] Correctly ignore auto preferred sizes in max-content contributions, as we clearly intended to in 1992cf3. Fixes #6455.

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -2919,6 +2919,7 @@ Flex Item Intrinsic Size Contributions</h4>
 	The <strong>main-size <a>max-content contribution</a> of a <a>flex item</a></strong>
 	is the larger of its <em>outer</em> <a>max-content size</a>
 	and outer <a>preferred size</a> (its 'width'/'height' as appropriate)
+	if that is not ''width/auto'',
 	clamped by its <a>flex base size</a> as a maximum (if it is not growable)
 	and/or as a minimum (if it is not shrinkable),
 	and then further clamped by its <a lt="min main size">min</a>/<a>max main size</a>.
@@ -3518,6 +3519,12 @@ Boris Zbarsky.
 Changes since the <a href="https://www.w3.org/TR/2018/CR-css-flexbox-1-20181119/">19 November 2018 CR</a></h3>
 
 	<ul>
+		<li id="change-2018-correctly-ignore-auto">
+			Correctly ignore ''width/auto'' [=preferred sizes=]
+			in both min <em>and</em> max size contribution calculations.
+			(It was accidentally omitted from the max,
+			tho it shows up in the <a href="#change-2017-flex-min-contribution">changelog</a>...)
+
 		<li id="change-2018-move-order">
 			Moved the 'order' property to [[css-display-3]].