Workaround dependency on closure library in chromevox test utility.

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

Index: chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js
diff --git a/chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js b/chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js
index b58b152f2e733154b5d516dc335618700523d164..7cb837fc6ed0a976abfc5ffdb59f3c86e3c94c2f 100644
--- a/chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js
+++ b/chrome/browser/resources/chromeos/chromevox/walkers/walker_unittest_base.js
@@ -39,7 +39,11 @@ CvoxWalkerUnitTestBase.prototype = {
    * 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