Material PDF: Drastically reduce time required to stamp complex bookmark trees

chrome/browser/resources/pdf/elements/viewer-toolbar-dropdown/viewer-toolbar-dropdown.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function() {
   /**
    * Size of additional padding in the inner scrollable section of the dropdown.
    */
   var DROPDOWN_INNER_PADDING = 12;
 
@@ skipping 12 matching lines @@
 
       /** Icon to display when the dropdown is closed. */
       closedIcon: String,
 
       /** Icon to display when the dropdown is open. */
       openIcon: String,
 
       /** True if the dropdown is currently open. */
       dropdownOpen: {
         type: Boolean,
+        reflectToAttribute: true,
         value: false
       },
 
       /** Toolbar icon currently being displayed. */
       dropdownIcon: {
         type: String,
         computed: 'computeIcon_(dropdownOpen, closedIcon, openIcon)'
       },
 
       /** Lowest vertical point that the dropdown should occupy (px). */
@@ skipping 19 matching lines @@
 
     lowerBoundChanged_: function() {
       this.maxHeightValid_ = false;
       if (this.dropdownOpen)
         this.updateMaxHeight();
     },
 
     toggleDropdown: function() {
       this.dropdownOpen = !this.dropdownOpen;
       if (this.dropdownOpen) {
-        this.$.icon.classList.add('open');
         this.$.dropdown.style.display = 'block';
         if (!this.maxHeightValid_)
           this.updateMaxHeight();
-      } else {
-        this.$.icon.classList.remove('open');
       }
       this.cancelAnimation_();
       this.playAnimation_(this.dropdownOpen);
     },
 
     updateMaxHeight: function() {
       var scrollContainer = this.$['scroll-container'];
       var height = this.lowerBound -
           scrollContainer.getBoundingClientRect().top -
           DROPDOWN_INNER_PADDING;
@@ skipping 43 matching lines @@
 
     animateExit_: function() {
       return this.$.dropdown.animate([
             {transform: 'translateY(0)', opacity: 1},
             {transform: 'translateY(-5px)', opacity: 0}
           ], {duration: 100, easing: 'cubic-bezier(0.4, 0, 1, 1)'});
     }
   });
 
 })();