Auto merge of #15888 - emilio:caching, r=Ms2ger

style: Simplify style sharing code.

No functional changes, just some code cleanup.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/15888)
<!-- Reviewable:end -->

tests/unit/style/cache.rs

@@ -1,40 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-use std::cell::Cell;
-use style::cache::LRUCache;
-
-#[test]
-fn test_lru_cache() {
-    let one = Cell::new("one");
-    let two = Cell::new("two");
-    let three = Cell::new("three");
-    let four = Cell::new("four");
-
-    // Test normal insertion.
-    let mut cache: LRUCache<usize, Cell<&str>> = LRUCache::new(2); // (_, _) (cache is empty)
-    cache.insert(1, one);    // (1, _)
-    cache.insert(2, two);    // (1, 2)
-    cache.insert(3, three);  // (2, 3)
-
-    assert!(cache.find(&1).is_none());  // (2, 3) (no change)
-    assert!(cache.find(&3).is_some());  // (2, 3)
-    assert!(cache.find(&2).is_some());  // (3, 2)
-
-    // Test that LRU works (this insertion should replace 3, not 2).
-    cache.insert(4, four); // (2, 4)
-
-    assert!(cache.find(&1).is_none());  // (2, 4) (no change)
-    assert!(cache.find(&2).is_some());  // (4, 2)
-    assert!(cache.find(&3).is_none());  // (4, 2) (no change)
-    assert!(cache.find(&4).is_some());  // (2, 4) (no change)
-
-    // Test find_or_create.
-    cache.find_or_create(1, || { Cell::new("one") }); // (4, 1)
-
-    assert!(cache.find(&1).is_some()); // (4, 1) (no change)
-    assert!(cache.find(&2).is_none()); // (4, 1) (no change)
-    assert!(cache.find(&3).is_none()); // (4, 1) (no change)
-    assert!(cache.find(&4).is_some()); // (1, 4)
-}

tests/unit/style/lib.rs

@@ -23,7 +23,6 @@ extern crate test;
 
 mod animated_properties;
 mod attr;
-mod cache;
 mod keyframes;
 mod logical_geometry;
 mod media_queries;