[css-grid-1] Apply track alignment in available space estimations in …

…step 1 of grid sizing algo. #2697

css-grid-1/Overview.bs

@@ -3580,6 +3580,10 @@ Grid Sizing Algorithm</h3>
 			assume the <a>available space</a> that it would have
 			if any row with a <a>definite</a> <a>max track sizing function</a>
 			had that size and all other rows were infinite.
+			If both the <a>grid container</a> and all tracks have <a>definite</a> sizes,
+			also apply 'align-content' to find the final effective size
+			of any gaps spanned by such items;
+			otherwise ignore the effects of track alignment in this estimation.
 
 		<div class="issue">
 			Would it help to have <a href="https://lists.w3.org/Archives/Public/www-style/2016Jan/0128.html">heuristics</a>
@@ -4401,6 +4405,13 @@ Major Changes</h4>
 				</ul>
 			</blockquote>
 
+		<li id="change-2017-track-alignment-sizing">
+			Better incorporated the alignment of tracks
+			('align-content'/'justify-content')
+			into the track sizing algorithm.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2557">Issue 2557</a>,
+			 <a href="https://github.com/w3c/csswg-drafts/issues/2697">Issue 2697</a>)
+
 		<li id="change-2017-repeat-serialization">
 			Require the used value of a track listing
 			to be serialized without using ''repeat()'' notation.