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
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Implement MutationObserver childList mutations
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Source-Repo: https://github.com/servo/servo
Source-Revision: 323760f47e79b49ef8db4484cca1969bc26b5413
Rebased from #16668.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix (partially) #6633
- [X] There are tests for these changes
Source-Repo: https://github.com/servo/servo
Source-Revision: 5da0aa9f11b7b1c2dc8b5adf178eebafa92d1849
