Roll third_party/polymer.

third_party/polymer/v1_0/components-chromium/iron-dropdown/iron-dropdown-scroll-manager-extracted.js

 (function() {
     'use strict';
 
     /**
      * The IronDropdownScrollManager is intended to provide a central source
      * of authority and control over which elements in a document are currently
      * allowed to scroll.
      */
 
     Polymer.IronDropdownScrollManager = {
@@ skipping 143 matching lines @@
             if (this._composedTreeContains(distributedNodes[nodeIndex], child)) {
               return true;
             }
           }
         }
 
         return false;
       },
 
       _scrollInteractionHandler: function(event) {
+        var scrolledElement =
+            /** @type {HTMLElement} */(Polymer.dom(event).rootTarget);
         if (Polymer
               .IronDropdownScrollManager
-              .elementIsScrollLocked(Polymer.dom(event).rootTarget)) {
+              .elementIsScrollLocked(scrolledElement)) {
           if (event.type === 'keydown' &&
               !Polymer.IronDropdownScrollManager._isScrollingKeypress(event)) {
             return;
           }
 
           event.preventDefault();
         }
       },
 
       _lockScrollInteractions: function() {
@@ skipping 30 matching lines @@
         document.body.style.overflowY = this._originalBodyStyles.overflowY;
 
         document.removeEventListener('wheel', this._scrollInteractionHandler, true);
         document.removeEventListener('mousewheel', this._scrollInteractionHandler, true);
         document.removeEventListener('DOMMouseScroll', this._scrollInteractionHandler, true);
         document.removeEventListener('touchmove', this._scrollInteractionHandler, true);
         document.removeEventListener('keydown', this._scrollInteractionHandler, true);
       }
     };
   })();