[css-flexbox] Rearrange the multi-line cross-size stuff, since there's an uncontroversial answer for row flexboxes.

Author: tabatkins

css-flexbox/Overview.bs

@@ -2751,7 +2751,16 @@ Intrinsic Sizes</h3>
 	The <dfn>min-content cross size</dfn> and  <dfn>max-content cross size</dfn> of a <a>single-line</a> <a>flex container</a>
 	is the largest <a>min-content contribution</a> or <a>max-content contribution</a> (respectively)
 	of its <a>flex items</a>.
-	For a <a>multi-line</a> <a>flex container</a>, ...
+	For a <a>multi-line</a> <a>flex container</a>,
+	the <a>min-content cross size</a>/<a>max-content cross size</a>
+	are the sum of the flex line cross sizes
+	resulting from sizing the flex container under a <a>cross-axis</a> <a>min-content constraint</a>/<a>max-content constraint</a>, respectively.
+
+	Issue: Current browsers set the flex container’s inner size
+	to the size of the largest min-content contribution,
+	instead of summing the lines.
+	This is clearly wrong,
+	as it is guaranteed to cause overflow if there are multiple lines.
 
 	<div class="issue">
 		In an ideal world, the multi-line cross size would be calculated by, one by one,
@@ -2765,13 +2774,9 @@ Intrinsic Sizes</h3>
 		and then shrink-to-fit sizing everything into that much available space.
 		Is this approximation sufficiently useful to specify?
 		Can we do better?
-
-		Current browsers also set the *flex container's* inner size to that largest value,
-		which is clearly wrong, as it is guaranteed to cause overflow if there are multiple lines.
-		We would need to require the cross-size to be the sum of the line's cross sizes
-		after doing item layout and linebreaking as outlined above.
 	</div>
 
+
 	The <strong>main-size <a lt="min-content contribution">min-content</a>/<a>max-content contribution</a> of a <a>flex item</a></strong>
 	is its outer <a lt="min-content size">min-content</a>/<a>max-content size</a>,
 	clamped by its <a>flex base size</a> as a maximum (if it is not growable)