[css-grid-1] Handle division by zero case for distributing intrinsic …

…item space to flexible tracks. #3694

css-grid-1/Overview.bs

@@ -4164,6 +4164,9 @@ Resolve Intrinsic Track Sizes</h3>
 					distributing space <em>only</em> to <a>flexible tracks</a>
 					(i.e. treating all other tracks as having a <a>fixed sizing function</a>)
 				<li>
+					if the sum of the <a>flexible sizing functions</a>
+					of all <a>flexible tracks</a> spanned by the item
+					is greater than zero,
 					distributing space to such tracks
 					according to the ratios of their <a>flexible sizing functions</a>
 					rather than distributing space equally
@@ -4661,6 +4664,19 @@ Major Changes</h4>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/3638">Issue 3638</a>,
 			 <a href="https://github.com/w3c/csswg-drafts/issues/3665">Issue 3665</a>)
 
+		<li id="change-2018-flex-zero-sum">
+			Don't divide by zero when <a lt="distribute extra space">distributing extra space</a>
+			across <a>flexible tracks</a>
+			when the sum of their <a>flexible sizing functions</a> is zero.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3694">Issue 3694</a>)
+			<blockquote>
+				<p><ins>if the sum of the <a>flexible sizing functions</a>
+				of all <a>flexible tracks</a> spanned by the item
+				is greater than zero,</ins>
+				distributing space to such tracks
+				according to the ratios of their <a>flexible sizing functions</a>
+				rather than distributing space equally
+			</blockquote>
 	</ul>
 
 <h4 id="clarify-2017">