Workaround dependency on closure library in chromevox test utility.

chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js

 // 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.
 
 GEN_INCLUDE(['../testing/chromevox_unittest_base.js']);
 
 /**
  * Base class for walker test fixtures.
  * @constructor
  * @extends {ChromeVoxUnitTestBase}
@@ skipping 21 matching lines @@
       document.body.removeChild(document.body.lastChild);
     }
 
     this.walker = this.newWalker();
   },
 
   /**
    * Returns a new walker appropriate for the child test.
    * @return {!cvox.AbstractWalker} The walker instance.
    */
-  newWalker: goog.abstractMethod,
+  // Closure library is not available when this literal is evaluated, so
+  // we can't use goog.abstractMethod here.
+  newWalker: function() {
+    throw Error('newWalker not implemented.');
+  },
 
   /**
    * Makes testing much less verbose. Executes the command on the
    * selection, then asserts that for all the parameters passed in desc,
    * the new selection matches. Returns the new selections if assertion passes.
    * NOTE: If you change the parameters here, you should also change the
    * whitelist above.
    * @param {!cvox.CursorSelection} sel The selection.
    * @param {!string|!cvox.CursorSelection} opt_cmdOrDest The command to
    *  execute, or the override returned selection.
@@ skipping 172 matching lines @@
    */
   TEST_F(testFixture, 'testEmptyBody', function() {
     var sel = cvox.CursorSelection.fromBody();
 
     // Testing for infinite loop. If one exists, this test will fail by timing
     // out.
     var sync = this.walker.sync(sel);
     var next = this.walker.next(sel);
   });
 };