sync and which return async, move the handling of alternates more completely
into the CSSLoader, make it possible for observers to tell whether the load
actually succeeded. Bug 293825, r+sr=peterv
and removed via the DOM. Clean up the nsIDocument stylesheet accessors. Clean
up nsIDocumentObserver stylesheet stuff a bit. Make style sheets visible in
the CSSOM (though not completely accessible) from the moment the load is kicked
off. Make us have sheet objects that can be manipulated via CSSOM even for
failed loads. Bug 107567, bug 47734, bug 57225, bug 178407.
r=sicking, sr=peterv.