[css-flexbox] Fix min/max-content cross-size for single-line flexboxes.

Author: tabatkins

css-flexbox/Overview.bs

@@ -2748,9 +2748,10 @@ Intrinsic Sizes</h3>
 	it is simply the largest <a>min-content contribution</a>
 	of all the <a>flex items</a> in the <a>flex container</a>.
 
-	The <dfn>min-content cross size</dfn> and  <dfn>max-content cross size</dfn> of a flex container
-	are the <a>cross size</a> of the flex container
-	after performing layout into the given available <a>main-axis</a> space and infinite available <a>cross-axis</a> space.
+	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>, ...
 
 	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>,