[menus] Make sure only one sub menu shows

Changes the logic that shows a sub menu to check if any other sub menu
is showing, and if so, hide it before showing the new sub menu.

Bug: 1100177
Change-Id: I33527c776bdff7cb0d7d9a452a0fe13b8df60434
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2277376Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Alex Danilo <adanilo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784350}

ui/file_manager/file_manager/foreground/js/ui/multi_menu.js

@@ -293,6 +293,16 @@ cr.define('cr.ui', () => {
       switch (e.type) {
         case 'activate':
         case 'mouseover':
+          // Hide any other sub menu being shown.
+          const showing = /** @type {cr.ui.MenuItem} */ (
+              this.querySelector('cr-menu-item[sub-menu-shown]'));
+          if (showing && showing !== item) {
+            showing.removeAttribute('sub-menu-shown');
+            const shownSubMenu = this.getSubMenuFromItem(showing);
+            if (shownSubMenu) {
+              shownSubMenu.hide();
+            }
+          }
           item.setAttribute('sub-menu-shown', 'shown');
           this.positionSubMenu_(item, subMenu);
           subMenu.show();