[css-grid-3][masonry] Link to dense packing issue

Author: fantasai

css-grid-3/Overview.bs

@@ -286,6 +286,14 @@ Auto Flow Directions: the 'grid-auto-flow' property</h4>
 
 	ISSUE: Should that be the case, or should we follow the 'grid-auto-flow' axis always
 	(so it would fill similar to flexbox, but with explicitly-sized tracks)?
+
+	ISSUE(9326):
+	Should <css>dense</css> packing apply to masonry?
+	It's much more expensive in masonry,
+	as you have to lay out the element in every possible gap spot
+	to see if it's short enough to fit;
+	Grid gets to just juggle some integers.
+
 </section>
 
 <section class="option masonry">