Allow creating new folders while scanning.

File changes (e.g. file creation) within the current directory would
trigger a rescan. This causes file changes to disable "New folder". This
causes flickering of the new folder menu item and button for multi-file
operations in the current directory. Avoid this by allowing new folder
while scanning.

Bug: 618002
Change-Id: I5943deeb0186ab425824eeb70ed69414e702da42
Reviewed-on: https://chromium-review.googlesource.com/c/1347633Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610282}

ui/file_manager/file_manager/foreground/js/file_manager_commands.js

@@ -746,7 +746,7 @@ CommandHandler.COMMANDS_['new-folder'] = (function() {
       var directoryEntry = fileManager.getCurrentDirectoryEntry();
       event.canExecute = !fileManager.directoryModel.isReadOnly() &&
           !fileManager.namingController.isRenamingInProgress() &&
-          !directoryModel.isSearching() && !directoryModel.isScanning() &&
+          !directoryModel.isSearching() &&
           CommandUtil.hasCapability([directoryEntry], 'canAddChildren');
       event.command.setHidden(false);
     }