[css-grid-2] Added issue for masonry layout.

Author: tabatkins

css-grid-2/Overview.bs

@@ -189,3 +189,42 @@ Subgrids</h2>
 			Since <a>subgrids</a> can be placed before their contents are placed,
 			their lines automatically receive the line names specified on the parent <a>grid</a>.
 	</ul>
+
+<!-- Big Text: masonry -->
+
+<h2 id=masonry>
+Masonry Layout</h2>
+
+<div class=issue>
+	People have been trying to use CSS for <a href="https://github.com/w3c/csswg-drafts/issues/1009#issuecomment-278095001">masonry layouts</a> for over a decade,
+	and it doesn't seem to have slowed,
+	so it's probably not just a layout fad.
+	Would probably be worthwhile to address officially.
+
+	As far as I can tell,
+	this is best done as a Grid feature;
+	some of the features I've seen in masonry libraries
+	(like large items spanning multiple masonry tracks)
+	make Flexbox inappropriate.
+	This also would reuse *so many* Grid features
+	that it would be a shame to put together a brand new layout spec for it.
+
+	No clue what it would look like yet, tho.
+	In handwavey terms, it's a grid that's only gridded
+	"in one dimension",
+	and free-flows in the other,
+	with auto-flow.
+
+	Note that this is actually 100% possibly with Grid today,
+	if your items are of known height,
+	by making thousands of 1px tall rows,
+	and setting the items' row-span to be equal to their height in px.
+	(Or some lower-res multiple, like 10px rows.)
+	Dense row auto-flow then magically makes Masonry happen.
+	This is just a terrible hack that runs into memory/CPU issues
+	due to the large number of rows.
+	It suggests, tho,
+	that making it work properly
+	is mostly a matter of relaxing some constraints,
+	rather than adding entirely new behavior.
+</div>