Conform selector used in focus manager of history to <cr-menu> element.

The issue was caused by a oversight of crrev.com/805713003.
As the menu was not treated as focus parent, 'focus' event was dispatched with the text-field as an target. This make the menu hidden just after the menu is shown.
This CL corrects the selector to make the menu focus parent.

BUG=444480
TEST=go through repro steps written in the issue

Review URL: https://codereview.chromium.org/822663003

Cr-Commit-Position: refs/heads/master@{#309610}

chrome/browser/resources/history/history_focus_manager.js

@@ -22,7 +22,7 @@ HistoryFocusManager.prototype = {
   /** @override */
   getFocusParent: function() {
     return document.querySelector('#overlay .showing') ||
-        document.querySelector('menu:not([hidden])') ||
+        document.querySelector('cr-menu:not([hidden])') ||
         $('history-page');
   },
 };