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.
In a later PR, DomRoot<T> will become a type alias of Root<Dom<T>>,
where Root<T> will be able to handle all the things that need to be
rooted that have a stable traceable address that doesn't move for the
whole lifetime of the root. Stay tuned.
PerformanceObserverInit.buffered
Per #18108, add `buffered` flag in the `PerformanceObserverInit` dict.
Per W3C spec, when `buffered` is set, `PerformanceObserver.observe()` method adds the entries buffered in the `Performance` instance into the observer's entry buffer.
One step is the implementation of the [filter by name and type](https://w3c.github.io/performance-timeline/#filter-buffer-by-name-and-type) algorithm. Don't think that the sort operation is useful in this case, but the spec states that this algorithm is to be used.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#18108
- [X] These changes do not require tests (yet) because the timeline API is not powered.
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