[css-flexbox] Allow flex items with indefinite flex size to be definite wrt resolving percentages inside them. w3c#1679.

Author: fantasai

css-flexbox/Overview.bs

@@ -2736,10 +2736,11 @@ Definite and Indefinite Sizes</h3>
 			and is considered <a>definite</a>.
 
 		<li>
-			If a <a>flex item</a> has a <a>definite</a> <a>flex basis</a>
-			and the <a>flex container</a> has a <a>definite</a> <a>main size</a>,
-			its post-flexing main size is treated as <a>definite</a>
-			(even though it might technically rely on the sizes of <a>indefinite</a> siblings to resolve its flexed main size).
+			If the <a>flex container</a> has a <a>definite</a> <a>main size</a>,
+			a <a>flex item</a>’s post-flexing <a>main size</a>
+			is treated as <a>definite</a>,
+			even though it can rely on the <a>indefinite</a> sizes
+			of any flex items in the same line.
 
 		<li>
 			Once the cross size of a flex line has been determined,
@@ -3434,6 +3435,18 @@ Substantive Changes and Bugfixes</h4>
 				and/or as a minimum (if it is not shrinkable),
 				and then further clamped by its <a lt="min main size property">min</a>/<a>max main size properties</a>.
 			</blockquote>
+		<li id="change-2017-definite-basis">
+			Since at least two implementations ended up
+			allowing percentages inside flex items with indefinite flex basis to resolve anyway,
+			removed the condition requiring definite flex basis.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/1679">Issue 1679</a>)
+			<blockquote>
+				<p>If <del>a <a>flex item</a> has a <a>definite</a> <a>flex basis</a>
+				and</del> the <a>flex container</a> has a <a>definite</a> <a>main size</a>,
+				<del>its</del> <ins>a <a>flex item</a>’s</ins> post-flexing main size is treated as <a>definite</a>
+				(even though it might technically rely on the <del>sizes of <a>indefinite</a> siblings to resolve its flexed main size</del>
+				the <a>indefinite</a> sizes of any flex items in the same line).
+			</blockquote>
 		<li id="change-2016-align-self-as-specified">
 			For ease of implementation, ''align-self/auto'' value of 'align-self' now computes to itself always.
 			See <a href="change-2015-align-self-auto">related previous change</a>