DevTools: add more jsdocs to NetworkPanel.

Source/devtools/front_end/timeline/TimelineView.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 689 matching lines @@
         }
     },
 
     _adjustScrollPosition: function(totalHeight)
     {
         // Prevent the container from being scrolled off the end.
         if ((this._scrollTop + this._containerElementHeight) > totalHeight + 1)
             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()
     {
         this._hideQuadHighlight();
     },
 
     /**
      * @param {?Event} e
      */
@@ skipping 567 matching lines @@
             this._element.classList.remove("hidden");
         } else
             this._element.classList.add("hidden");
     },
 
     _dispose: function()
     {
         this._element.remove();
     }
 }