Fix some ChromeVox Closure compiler errors.

chrome/browser/resources/chromeos/chromevox/walkers/table_walker.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.
 
 /**
  * @fileoverview A class for walking tables.
  * NOTE: This class has a very different interface than the other walkers.
  * This means it does not lend itself easily to e.g. decorators.
  * TODO (stoarca): This might be able to be fixed by breaking it up into
  * separate walkers for cell, row and column.
@@ skipping 366 matching lines @@
 /**
  * Wrapper for going to somewhere so that boilerplate is not repeated.
  * @param {!cvox.CursorSelection} sel The selection from which to base the
  * movement.
  * @param {function(Array<number>):boolean} f The function to use for moving.
  * Returns true on success and false on failure.
  * @return {cvox.CursorSelection} The resulting selection.
  * @private
  */
 cvox.TableWalker.prototype.goTo_ = function(sel, f) {
+  if (!sel.end.node) {
+    return null;
+  }
   this.tt.initialize(this.getTableNode_(sel));
   var position = this.tt.findNearestCursor(sel.end.node);
   if (!position) {
     return null;
   }
   this.tt.goToCell(position);
   if (!f(position)) {
     return null;
   }
   return cvox.CursorSelection.fromNode(this.tt.getCell()).
@@ skipping 16 matching lines @@
  * @return {Array<number>} The position [x, y] of the selection.
  * @private
  */
 cvox.TableWalker.prototype.syncPosition_ = function(sel) {
   var tableNode = this.getTableNode_(sel);
   this.tt.initialize(tableNode);
   // we need to align the TraverseTable with our sel because our walker
   // uses parts of it (for example isSpanned relies on being at a specific cell)
   return this.tt.findNearestCursor(sel.end.node);
 };