[css-font-loading-3] Align with Web IDL specification

Author: autokagami

css-font-loading-3/Overview.bs

@@ -443,7 +443,7 @@ The <code>FontFaceSet</code> Interface</h2>
 
 		enum FontFaceSetLoadStatus { "loading", "loaded" };
 
-		callback ForEachCallback = void (FontFace font, long index, FontFaceSet self);
+		callback ForEachCallback = undefined (FontFace font, long index, FontFaceSet self);
 
 		[Exposed=(Window,Worker)]
 		interface FontFaceSet : EventTarget {
@@ -453,7 +453,7 @@ The <code>FontFaceSet</code> Interface</h2>
 			setlike<FontFace>;
 			FontFaceSet add(FontFace font);
 			boolean delete(FontFace font);
-			void clear();
+			undefined clear();
 
 			// events for when loading state changes
 			attribute EventHandler onloading;