Fix PDF viewer console errors for Polymer2 migration

Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I09abc82ecd2ab71850a70c65a9a2decfcc011fe3
Bug: 849476
Reviewed-on: https://chromium-review.googlesource.com/1086236Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564787}

chrome/browser/resources/pdf/elements/viewer-bookmark/viewer-bookmark.js

@@ -40,18 +40,19 @@ Polymer({
 
     childrenShown: {type: Boolean, reflectToAttribute: true, value: false},
 
-    keyEventTarget: {
-      type: Object,
-      value: function() {
-        return this.$.item;
-      }
-    }
+    /** @type {?HTMLElement} The target for the key bindings below. */
+    keyEventTarget: Object,
   },
 
   behaviors: [Polymer.IronA11yKeysBehavior],
 
   keyBindings: {'enter': 'onEnter_', 'space': 'onSpace_'},
 
+  /** @override */
+  attached: function() {
+    this.keyEventTarget = this.$.item;
+  },
+
   bookmarkChanged_: function() {
     this.$.expand.style.visibility =
         this.bookmark.children.length > 0 ? 'visible' : 'hidden';

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

@@ -42,17 +42,18 @@ Polymer({
     /** Lowest vertical point that the dropdown should occupy (px). */
     lowerBound: {type: Number, observer: 'lowerBoundChanged_'},
 
-    /**
-     * True if the max-height CSS property for the dropdown scroll container
-     * is valid. If false, the height will be updated the next time the
-     * dropdown is visible.
-     */
-    maxHeightValid_: false,
-
     /** Current animation being played, or null if there is none. */
     animation_: Object
   },
 
+  /**
+   * True if the max-height CSS property for the dropdown scroll container
+   * is valid. If false, the height will be updated the next time the
+   * dropdown is visible.
+   * @private {boolean}
+   */
+  maxHeightValid_: false,
+
   computeIcon_: function(dropdownOpen, closedIcon, openIcon) {
     return dropdownOpen ? openIcon : closedIcon;
   },

chrome/browser/resources/pdf/elements/viewer-zoom-toolbar/viewer-zoom-button.js

@@ -53,7 +53,7 @@ Polymer({
   },
 
   computeVisibleTooltip_: function(tooltips, activeIndex) {
-    return tooltips[activeIndex];
+    return tooltips === undefined ? '' : tooltips[activeIndex];
   },
 
   delayChanged_: function() {