Bug 1631721 - Vendor the hashbrown crate r=manishearth

This is the hash map implementation now used in the Rust standard library:

* https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html#a-new-hashmapk-v-implementation
* rust-lang/rust#58623
* https://crates.io/crates/hashbrown

Differential Revision: https://phabricator.services.mozilla.com/D71740

servo/components/style/Cargo.toml

@@ -40,6 +40,7 @@ encoding_rs = {version = "0.8", optional = true}
 euclid = "0.20"
 fallible = { path = "../fallible" }
 fxhash = "0.2"
+hashbrown = "0.7"
 hashglobe = { path = "../hashglobe" }
 html5ever = {version = "0.24", optional = true}
 indexmap = "1.0"

third_party/rust/ahash/.cargo-checksum.json

@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"f0e25e3e6f839a66910d21529e8ba1912fcc86985869aa1e0bc82615bcc9c616","LICENSE-APACHE":"a60eea817514531668d7e00765731449fe14d059d3249e0bc93b36de45f759f2","LICENSE-MIT":"ff8f68cb076caf8cefe7a6430d4ac086ce6af2ca8ce2c4e5a2004d4552ef52a2","README.md":"cae69bc8ba7fee044c48b7126a5facb831c29913753f7daec85a057d6d2b33fd","rustfmt.toml":"e090969e99df9360705680cc0097cfaddae10c22dc2e01470592cf3b9787fd36","src/aes_hash.rs":"e6fbcaf7d5a0153b98c7e70f8dd15cb56b1e4b9ae98747c05c12858342065ea6","src/convert.rs":"45c69b65982a95cc78d1b4e54c662be7d852aa03366acf57699e55a62ecb8930","src/fallback_hash.rs":"3d398c24197e7413461edbd79821aba118284dcdd0f1eaa01672fb717e561601","src/folded_multiply.rs":"f3a6ddc1db0655cc1ca775b8370175b3a098ed60e31bf15573879d2ab6870acb","src/hash_map.rs":"36bf0b13e334d7cedbf83e4822438098b227e7c7e381abe5e1eeac1ff6caa209","src/hash_quality_test.rs":"ecb76478989eb3b96e4a299aeccb0d75ba53d13b2c11e5a3c8de15d466a7476a","src/hash_set.rs":"4289672c142e314a0bfc6535b5e8f5e07cc78b60c0c7b308a43fa361eca6ddea","src/lib.rs":"ad3538e0a10bba5fba2f7364f2e0673a62c99b617b7c2fd96232100042a64781","src/random_state.rs":"85749d2b2c915c29c129f609cc22270ab1902a436bfc3997002adecf93c62406","tests/bench.rs":"a206178c8fb2a9756fb4292c44a3a4355143915217018e253930efd1575e99fb","tests/map_tests.rs":"68b81bcef528a83b8b786baad15db8cae13e5ca1db1e595e5aa74bdbf8d8115b","tests/nopanic.rs":"bc54a25d271c690ed49f6eb896e377bfb96217d29eb2c198052771714e972a56"},"package":"0989268a37e128d4d7a8028f1c60099430113fdbc70419010601ce51a228e4fe"}

third_party/rust/ahash/Cargo.toml

@@ -0,0 +1,90 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "ahash"
+version = "0.3.2"
+authors = ["Tom Kaitchuck <Tom.Kaitchuck@gmail.com>"]
+description = "A non-cryprographic hash function using AES-NI for high performance"
+documentation = "https://docs.rs/ahash"
+readme = "README.md"
+keywords = ["hash", "hashmap", "aes", "aes-ni", "no-std"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/tkaitchuck/ahash"
+[package.metadata.docs.rs]
+features = ["std"]
+rustc-args = ["-C", "target-feature=+aes"]
+rustdoc-args = ["-C", "target-feature=+aes"]
+[profile.bench]
+opt-level = 3
+lto = "fat"
+codegen-units = 1
+debug = false
+debug-assertions = false
+
+[profile.release]
+opt-level = 3
+lto = "fat"
+codegen-units = 1
+debug = false
+debug-assertions = false
+
+[profile.test]
+opt-level = 2
+
+[lib]
+name = "ahash"
+path = "src/lib.rs"
+test = true
+doctest = true
+bench = true
+doc = true
+
+[[bench]]
+name = "ahash"
+path = "tests/bench.rs"
+harness = false
+
+[[bench]]
+name = "map"
+path = "tests/map_tests.rs"
+harness = false
+[dependencies.const-random]
+version = "0.1.6"
+optional = true
+[dev-dependencies.criterion]
+version = "0.3.0"
+features = ["real_blackbox"]
+
+[dev-dependencies.fnv]
+version = "1.0.5"
+
+[dev-dependencies.fxhash]
+version = "0.2.1"
+
+[dev-dependencies.hex]
+version = "0.3.2"
+
+[dev-dependencies.no-panic]
+version = "0.1.10"
+
+[dev-dependencies.rand]
+version = "0.6.5"
+
+[dev-dependencies.seahash]
+version = "3.0.5"
+
+[features]
+compile-time-rng = ["const-random"]
+default = ["compile-time-rng", "std"]
+std = []