http://www.robohornet.org gives a score of 101.36 on master, and 102.68 with this PR. The latter is slightly better, but probably within noise level. So it looks like this PR does not affect DOM performance.
This is expected since `Box::new` is defined as:
```rust
impl<T> Box<T> {
#[inline(always)]
pub fn new(x: T) -> Box<T> {
box x
}
}
```
With inlining, it should compile to the same as box syntax.
Source-Repo: https://github.com/servo/servo
Source-Revision: a9022be0c3e30249845ca5947ac0c0a6743c7991
Globals in that PR are now represented by the fake IDL interface `GlobalScope`.
Source-Repo: https://github.com/servo/servo
Source-Revision: a6e4b5bb86ad707a0863acff87344ca4239cfd2c
