I found that notify_register_dispatch is used in WTF and JSC too. We should have one wrapper around notify_register_dispatch in WTF (PAL::registerNotifyCallback thing) and use it everywhere in WebKit. It is nice since we can grep all the registrations with PAL::registerNotifyCallback.
I was adding a callback for my debugging purpose of memory thing, and I noticed that WTF uses notify_register_dispatch, while PAL has PAL::registerNotifyCallback.