DevTools: add more jsdocs to NetworkPanel.

Source/devtools/front_end/timeline/TimelineView.js

Index: Source/devtools/front_end/timeline/TimelineView.js
diff --git a/Source/devtools/front_end/timeline/TimelineView.js b/Source/devtools/front_end/timeline/TimelineView.js
index a0842483178b755d3ddb1a1f64aa742834ff0234..7dd1dbdbd027e11145c0df0293d964c014961d99 100644
--- a/Source/devtools/front_end/timeline/TimelineView.js
+++ b/Source/devtools/front_end/timeline/TimelineView.js
@@ -707,12 +707,16 @@ WebInspector.TimelineView.prototype = {
             this._containerElement.scrollTop = (totalHeight - this._containerElement.offsetHeight);
     },
 
-    _getPopoverAnchor: function(element)
+    /**
+     * @param {!Element} element
+     * @param {!Event} event
+     * @return {!Element|!AnchorBox|undefined}
+     */
+    _getPopoverAnchor: function(element, event)
     {
         var anchor = element.enclosingNodeOrSelfWithClass("timeline-graph-bar");
         if (anchor && anchor._tasksInfo)
             return anchor;
-        return null;
     },
 
     _mouseOut: function()