[css-font-loading] when firing a font load event, only include faces still present in the set.

Author: tabatkins

css-font-loading/Overview.bs

@@ -558,7 +558,8 @@ Events</h3>
 
 	<ol>
 		<li>
-			The {{FontFaceSetLoadEvent/fontfaces}} attribute is initialized to the given list of {{FontFace}} objects.
+			The {{FontFaceSetLoadEvent/fontfaces}} attribute is initialized to
+			the result of filtering <var>font faces</var> to only contain {{FontFace}} objects contained in <var>target</var>.
 	</ol>
 
 	Whenever one or more {{FontFace}} objects within a given {{FontFaceSet}}