servo: Merge #17487 - Correct bloom hash bitpacking documentation (from MattWis:patch-1); r=emilio

The two 12 bit keys add to 24 bits, which leaves 8 bits free in each word. (And 8 * 3 = 24, to pack in the fourth hash.)

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I have never actually built servo, but I'm pretty sure that's not necessary for a 1 line comment-only change

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Source-Repo: https://github.com/servo/servo
Source-Revision: 56cc39433f5dc902f80080060a4b6522383254e5

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : b71cd93bbc7e77fb8e3971f6ce7ff1e509d7d978

servo/components/selectors/bloom.rs

@@ -7,7 +7,7 @@
 use fnv::FnvHasher;
 use std::hash::{Hash, Hasher};
 
-// The top 12 bits of the 32-bit hash value are not used by the bloom filter.
+// The top 8 bits of the 32-bit hash value are not used by the bloom filter.
 // Consumers may rely on this to pack hashes more efficiently.
 pub const BLOOM_HASH_MASK: u32 = 0x00ffffff;
 const KEY_SIZE: usize = 12;