Why have createEmptyCSSStyleSheet()?

[domenic]

Seems nicer to just have one sync constructor, createCSSStyleSheetSync(''). Maybe even make the string optional so you don't need to pass an empty string. (Although I guess passing nothing will be equivalent to passing 'undefined' which will be treated as a no-op ^_^.)

[tabatkins]

It's a spandrel from before when we couldn't make a sync constructor. There's no need to have it anymore.

(And passing nothing can work, we just need to give the argument a default value in IDL. ^_^)