auto merge of #4938 : nnethercote/servo/dont-clone-bloom-filter, r=Ms2ger

When a cached bloom filter is found during traversal, there are two
cases, both of which currently do unnecessary allocations. This patch
avoids these allocations. In the process, it renders correct two
previously-incorrect comments, and moves one of those comments into a
better spot.

While scrolling moderately fast all the way through the "Guardians of
the Galaxy" Wikipedia page, this patch (a) avoids 1.2 million calls to
`clone()` and (b) replaces 111,000 `BloomFilter::new()` calls with
`clear()` calls.

0 files changed, 0 insertions, 0 deletions