[Switch Access] Only jump to modal dialogs if they are valid groups

Do not navigate to a node which Switch Access users can't interact with.
Fixes a bug where users were entering the dropdown options in a combo
box without the options being shown.

AX-Relnotes: n/a.
Bug: 1095221
Change-Id: Ia7418ca610bc065f525ea5fc9684489f506196d2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2295802Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#789140}

chrome/browser/resources/chromeos/accessibility/switch_access/navigation_manager.js

@@ -244,8 +244,10 @@ class NavigationManager {
    * @private
    */
   onModalDialog_(event) {
-    const menuRoot = ModalDialogRootNode.buildTree(event.target);
-    this.jumpTo_(menuRoot);
+    const modalRoot = ModalDialogRootNode.buildTree(event.target);
+    if (modalRoot.isValidGroup()) {
+      this.jumpTo_(modalRoot);
+    }
   }
 
   /**