MD Downloads: reduce the size of the ellided, displayed download URL

chrome/test/data/webui/md_downloads/layout_tests.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.
 
 suite('layout tests', function() {
   /** @type {!downloads.Manager} */
   var manager;
 
   setup(function() {
     PolymerTest.clearBody();
     manager = document.createElement('downloads-manager');
     document.body.appendChild(manager);
     assertEquals(manager, downloads.Manager.get());
   });
 
   test('long URLs ellide', function() {
     downloads.Manager.insertItems(0, [{
       file_name: 'file name',
       state: downloads.States.COMPLETE,
       url: 'a'.repeat(1000),
     }]);
 
     Polymer.dom.flush();
 
     var item = manager.$$('downloads-item');
     assertLT(item.$$('#url').offsetWidth, item.offsetWidth);
+    assertEquals(300, item.$$('#url').textContent.length);
   });
 });