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

chrome/browser/resources/md_history/constants.js

 // Copyright 2016 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.
 
 // Globals:
 /** @const */ var RESULTS_PER_PAGE = 150;
 
 /**
  * Amount of time between pageviews that we consider a 'break' in browsing,
  * measured in milliseconds.
  * @const
  */
 var BROWSING_GAP_TIME = 15 * 60 * 1000;
 
 /**
+ * Maximum length of a history item title. Anything longer than this will be
+ * cropped to fit within this limit. This value is large enough that it will not
+ * be noticeable in a 960px wide history-item.
+ * @const
+ */
+var TITLE_MAX_LENGTH = 300;
+
+/**
  * @enum {number}
  */
 var HistoryRange = {
   ALL_TIME: 0,
   WEEK: 1,
   MONTH: 2
 };