MD History: Trim long item titles to reduce effect on performance

chrome/browser/resources/md_history/history_item.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.
 
 cr.define('md_history', function() {
   var HistoryItem = Polymer({
     is: 'history-item',
 
     properties: {
       // Underlying HistoryEntry data for this item. Contains read-only fields
@@ skipping 63 matching lines @@
      * @param {string} search The search term associated with these results.
      * @private
      */
     cardTitle_: function(numberOfItems, historyDate, search) {
       if (!search)
         return this.item.dateRelativeDay;
 
       var resultId = numberOfItems == 1 ? 'searchResult' : 'searchResults';
       return loadTimeData.getStringF('foundSearchResults', numberOfItems,
           loadTimeData.getString(resultId), search);
+    },
+
+    /**
+     * Crop long item titles to reduce their effect on layout performance. See
+     * crbug.com/621347.
+     * @param {string} title
+     * @return {string}
+     */
+    cropItemTitle_: function(title) {
+      return (title.length > TITLE_MAX_LENGTH) ?
+          title.substr(0, TITLE_MAX_LENGTH) :
+          title;
     }
   });
 
   /**
    * Check whether the time difference between the given history item and the
    * next one is large enough for a spacer to be required.
    * @param {Array<HistoryEntry>} visits
    * @param {number} currentIndex
    * @param {string} searchedTerm
    * @return {boolean} Whether or not time gap separator is required.
    * @private
    */
   HistoryItem.needsTimeGap = function(visits, currentIndex, searchedTerm) {
     if (currentIndex >= visits.length - 1 || visits.length == 0)
       return false;
 
     var currentItem = visits[currentIndex];
     var nextItem = visits[currentIndex + 1];
 
     if (searchedTerm)
       return currentItem.dateShort != nextItem.dateShort;
 
     return currentItem.time - nextItem.time > BROWSING_GAP_TIME &&
         currentItem.dateRelativeDay == nextItem.dateRelativeDay;
   };
 
   return { HistoryItem: HistoryItem };
 });