[MD Bookmarks] Add keyboard navigation and selection to bookmark list.

third_party/polymer/v1_0/components-chromium/iron-list/iron-list-extracted.js

 (function() {
 
   var IOS = navigator.userAgent.match(/iP(?:hone|ad;(?: U;)? CPU) OS (\d+)/);
   var IOS_TOUCH_SCROLLING = IOS && IOS[1] >= 8;
   var DEFAULT_PHYSICAL_COUNT = 3;
   var HIDDEN_Y = '-10000px';
   var ITEM_WIDTH = 0;
   var ITEM_HEIGHT = 1;
   var SECRET_TABINDEX = -100;
 
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     },
 
     _isIndexVisible: function(idx) {
       return idx >= this.firstVisibleIndex && idx <= this.lastVisibleIndex;
     },
 
     _getPhysicalIndex: function(idx) {
       return this._physicalIndexForKey[this._collection.getKey(this._getNormalizedItem(idx))];
     },
 
+    focusItem: function(idx) {
+      this._focusPhysicalItem(idx);
+    },
+
     _focusPhysicalItem: function(idx) {
       if (idx < 0 || idx >= this._virtualCount) {
         return;
       }
       this._restoreFocusedItem();
       // scroll to index to make sure it's rendered
       if (!this._isIndexRendered(idx)) {
         this.scrollToIndex(idx);
       }
 
@@ skipping 122 matching lines @@
       this._focusPhysicalItem(this._focusedIndex + 1);
     },
 
     _didEnter: function(e) {
       this._focusPhysicalItem(this._focusedIndex);
       this._selectionHandler(e.detail.keyboardEvent);
     }
   });
 
 })();