Looks like applicationCache was disabled on purpose, see: https://bugs.webkit.org/attachment.cgi?id=426150&action=diff

It's absolutely insane. A lot of us work with different technologies and have to switch between various IDEs. Every single one of them, I can configure to behave roughly in the same predictable way, making switching between them seamless. All of them, except xcode. Because Apple apparently knows better and has to force their way onto others. Simple things like a predictable tab management, or even reliable automatic removal of trailing whitespace just don't function properly here.