Disable "New Folder" context menu item in search.

Add unit tests to cover more cases in context menus.

Bug: 31996780
Change-Id: I73443e09e81f0c747dd057dbc72ea6441cdd447e
diff --git a/src/com/android/documentsui/MenuManager.java b/src/com/android/documentsui/MenuManager.java
index 5bf360f..39ecbfa 100644
--- a/src/com/android/documentsui/MenuManager.java
+++ b/src/com/android/documentsui/MenuManager.java
@@ -175,9 +175,11 @@
     public void updateContextMenuForContainer(Menu menu) {
         MenuItem paste = menu.findItem(R.id.menu_paste_from_clipboard);
         MenuItem selectAll = menu.findItem(R.id.menu_select_all);
+        MenuItem createDir = menu.findItem(R.id.menu_create_dir);
 
         paste.setEnabled(mDirDetails.hasItemsToPaste() && mDirDetails.canCreateDoc());
         updateSelectAll(selectAll);
+        updateCreateDir(createDir);
     }
 
     /**