startup() arguments

[bill]

For performance, consider passing [an optional] parameter to startup() specifying the parent widget, and/or whether or not the parent widget will call resize() on the child (this).

That will avoid the getParent() call in startup().

Not sure if this change would have a performance impact or not. getParent() should be fast for something like MenuItem since the Menu is directly above it. getParent() for a widget deeply nested in a ContentPane will take longer, although that sounds like an uncommon case.