RootLayoutMgr.setDefaultLayout (alias)
Set the layout with the alias passed as argument to the default root layout

Sourcecode in RootLayoutMgr/objectFunctions.js:
1:   function setDefaultLayout(alias) {
2:      var l = root.layouts.get(alias);
3:      if (root.sys_layout != l)
4:         root.sys_layout = l;
5:      return;
6:   }