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third_party/polymer/components/iron-dropdown/iron-dropdown-scroll-manager.html

 <!--
 @license
 Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 
@@ skipping 13 matching lines @@
     /**
      * Used to avoid computing event.path and filter scrollable nodes (better perf).
      * @type {?EventTarget}
      */
     var lastRootTarget = null;
     /**
      * @type {!Array<Node>}
      */
     var lastScrollableNodes = [];
 
+    var scrollEvents = [
+      // Modern `wheel` event for mouse wheel scrolling:
+      'wheel',
+      // Older, non-standard `mousewheel` event for some FF:
+      'mousewheel',
+      // IE:
+      'DOMMouseScroll',
+      // Touch enabled devices
+      'touchstart',
+      'touchmove'
+    ];
+
     /**
      * 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 = {
 
       /**
        * The current element that defines the DOM boundaries of the
@@ skipping 148 matching lines @@
         if (event.targetTouches) {
           var touch = event.targetTouches[0];
           lastTouchPosition.pageX = touch.pageX;
           lastTouchPosition.pageY = touch.pageY;
         }
       },
 
       _lockScrollInteractions: function() {
         this._boundScrollHandler = this._boundScrollHandler ||
           this._scrollInteractionHandler.bind(this);
-        // Modern `wheel` event for mouse wheel scrolling:
-        document.addEventListener('wheel', this._boundScrollHandler, true);
-        // Older, non-standard `mousewheel` event for some FF:
-        document.addEventListener('mousewheel', this._boundScrollHandler, true);
-        // IE:
-        document.addEventListener('DOMMouseScroll', this._boundScrollHandler, true);
-        // Save the lastScrollableNodes on touchstart, to be used on touchmove.
-        document.addEventListener('touchstart', this._boundScrollHandler, true);
-        // Mobile devices can scroll on touch move:
-        document.addEventListener('touchmove', this._boundScrollHandler, true);
+        for (var i = 0, l = scrollEvents.length; i < l; i++) {
+          // NOTE: browsers that don't support objects as third arg will
+          // interpret it as boolean, hence useCapture = true in this case. 
+          document.addEventListener(scrollEvents[i], this._boundScrollHandler, {
+            capture: true,
+            passive: false
+          });
+        }
       },
 
       _unlockScrollInteractions: function() {
-        document.removeEventListener('wheel', this._boundScrollHandler, true);
-        document.removeEventListener('mousewheel', this._boundScrollHandler, true);
-        document.removeEventListener('DOMMouseScroll', this._boundScrollHandler, true);
-        document.removeEventListener('touchstart', this._boundScrollHandler, true);
-        document.removeEventListener('touchmove', this._boundScrollHandler, true);
+        for (var i = 0, l = scrollEvents.length; i < l; i++) {
+          // NOTE: browsers that don't support objects as third arg will
+          // interpret it as boolean, hence useCapture = true in this case.
+          document.removeEventListener(scrollEvents[i], this._boundScrollHandler, {
+            capture: true,
+            passive: false
+          });
+        }
       },
 
       /**
        * Returns true if the event causes scroll outside the current locking
        * element, e.g. pointer/keyboard interactions, or scroll "leaking"
        * outside the locking element when it is already at its scroll boundaries.
        * @param {!Event} event
        * @return {boolean}
        * @private
        */
@@ skipping 120 matching lines @@
           // Touch moves from right to left => scrolling goes right.
           info.deltaX = lastTouchPosition.pageX - touch.pageX;
           // Touch moves from down to up => scrolling goes down.
           info.deltaY = lastTouchPosition.pageY - touch.pageY;
         }
         return info;
       }
     };
   })();
 </script>