FWIW this was really helpful but didn’t quite get me there. Even with a fairly simple webpage, the resize on setting visibility still caused the white flash. Pages still don’t load when the browser is invisible, so Instead I use (pseudocode):
if(pageReady){
webComponent.setBounds(getLocalBounds());
} else {
const auto w = getWidth();
const auto h = getHeight();
webComponent.setBounds (w-1, h-1, w, h);
}