Add a forgotten ChromeVox test to the build system.

chrome/browser/resources/chromeos/chromevox/common/content_editable_extractor_test.unitjs

 // Copyright 2014 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../testing/chromevox_unittest_base.js']);
 
 /**
  * Test fixture.
  * @constructor
  * @extends {ChromeVoxUnitTestBase}
  */
 function CvoxContentEditableExtractorUnitTest() {}
 
 CvoxContentEditableExtractorUnitTest.prototype = {
   __proto__: ChromeVoxUnitTestBase.prototype,
 
   /** @override */
   closureModuleDeps: [
     'cvox.ContentEditableExtractor',
   ]
 };
 
+/**
+ * Helper function to set the selection
+ * @param {Node} startNode The base/start node of the range.
+ * @param {number} startOffset The 0-based character index of the start.
+ * @param {Node} endNode The extent/end node of the range.
+ * @param {number} endOffset The 0-based character index of the end.
+ */
+function setSelection(startNode, startOffset, endNode, endOffset) {
+  var r = document.createRange();
+  r.setStart(startNode, startOffset);
+  r.setEnd(endNode, endOffset);
+  var sel = window.getSelection();
+  sel.removeAllRanges();
+  sel.addRange(r);
+}
+
 TEST_F('CvoxContentEditableExtractorUnitTest', 'EmptyElement', function() {
   this.loadDoc(function() {/*!
     <div>
       <div id="textbox" contentEditable="true"></div>
     </div>
   */});
 
   var textbox = $('textbox');
   var extractor = new cvox.ContentEditableExtractor();
   extractor.update(textbox);
@@ skipping 267 matching lines @@
   extractor.update(textbox);
   assertEquals(7, extractor.getStartIndex());
   assertEquals(7, extractor.getEndIndex());
 
   // Beginning of third line.
   setSelection(threeTextNode, 0, threeTextNode, 0);
   extractor.update(textbox);
   assertEquals(8, extractor.getStartIndex());
   assertEquals(8, extractor.getEndIndex());
 });