This method returned the result of `RefCell<T>.try_borrow().is_some()`.
But it meant whether the state **is not** BorrowState::Writing.
This wrong is introduced by [1], Before it revision, this method had
returned whether the state is BorrowState::Writing or not.
This doesn't change callers of this method because git blames ([3], [4]) says
that the caller is introduced by [2] and [2] is introduced before [1].
[1]: 86d609abaf
[2]: 49234484d6
[3]: 2cc08f289a/components/script/dom/servohtmlparser.rs
[4]: a7e29939a1/components/script/dom/bindings/cell.rs
It also removes LiveDOMReferences destructor that it's a no-op but it contains an assert that was being violated causing an endless cycle of destructor calls ending up in a stack overflow.
This used to conflict with the util crate from the standard library, which
has long since been removed.
The import in layout has not been changed because of a conflict with the
util mod there.
This gets rid of a dubious transmute:
let val = mem::transmute::<&RefCell<T>, &T>(&self.base);
The code duplication will be reduced once rust-lang/rust#18131 is fixed.
This type simply wraps `RefCell<T>` to add the special method,
and introduce the method to return the pointer of the value contained in
itself, for used in layout task.
