Added unit tests for tree_walker and automation_predicate.

chrome/browser/resources/chromeos/switch_access/test_support.js

+// Copyright 2017 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.
+
+function TestSupport() {};
+
+TestSupport.prototype = {
+  /**
+   * Connect |parent| and |children| to each other.
+   *
+   * @param {!Object} parent
+   * @param {Array<Object>} children
+   */
+  setChildren: function(parent, children) {
+    // Connect parent to its children.
+    parent.children = children;
+    parent.firstChild = children[0];
+    parent.lastChild = children[children.length - 1];
+
+    for (let i = 0; i < children.length; i++) {
+      let child = children[i];
+
+      // Connect children to their parent.
+      child.parent = parent;
+
+      // Connect children to each other
+      if (i < children.length - 1)
+        child.nextSibling = children[i + 1];
+      if (i > 0)
+        child.previousSibling = children[i - 1];
+    }
+  },
+};