[cssom-view-1] adds details for handling scrollend event listeners

Author: Adam Argyle

cssom-view-1/Overview.bs

@@ -1684,6 +1684,17 @@ When asked to <dfn export for=Document>run the scroll steps</dfn> for a {{Docume
     1. Otherwise, <a>fire an event</a> named <a event>scroll</a> at <var>target</var>.
 1. Empty <var>doc</var>'s <a>pending scroll event targets</a>.
 
+Whenever scrolling is <a lt="scroll completed">completed</a>, the user agent must run these steps:
+
+1. If scrolling was done on a <a>viewport</a>, let <var>doc</var> be the <a>viewport’s</a> associated {{Document}} and <var>target</var> be the <a>viewport</a>.
+Otherwise, scrolling is done on an element and let <var>doc</var> be the element's <a>node document</a> and <var>target</var> be the element.
+1. If <var>target</var> is already in <var>doc</var>'s <a>pending scrollend event targets</a>, abort these steps.
+1. Append <var>target</var> to <var>doc</var>'s <a>pending scrollend event targets</a>.
+1. For each item <var>target</var> in <var>doc</var>'s <a>pending scrollend event targets</a>, in the order they were added to the list, run these substeps:
+
+    1. If <var>target</var> is a {{Document}}, <a>fire an event</a> named <a event>scrollend</a> that bubbles at <var>target</var>.
+    1. Otherwise, <a>fire an event</a> named <a event>scrollend</a> at <var>target</var>.
+1. Empty <var>doc</var>'s <a>pending scrollend event targets</a>.
 
 <h3 id=event-summary>Event summary</h3>