Implement OwningHandle in style.

I've also PR-ed this against upstream [1], but I don't want to block on that
in case it takes a while to be merged / published.

[1] https://github.com/Kimundi/owning-ref-rs/pull/15

tests/unit/style/Cargo.toml

@@ -13,6 +13,7 @@ doctest = false
 app_units = "0.3"
 cssparser = {version = "0.7", features = ["heap_size"]}
 euclid = "0.10.1"
+owning_ref = "0.2.2"
 parking_lot = "0.3"
 rustc-serialize = "0.3"
 selectors = "0.13"

tests/unit/style/lib.rs

@@ -9,6 +9,7 @@
 extern crate app_units;
 extern crate cssparser;
 extern crate euclid;
+extern crate owning_ref;
 extern crate parking_lot;
 extern crate rustc_serialize;
 extern crate selectors;
@@ -22,6 +23,7 @@ mod attr;
 mod cache;
 mod logical_geometry;
 mod media_queries;
+mod owning_handle;
 mod parsing;
 mod properties;
 mod selector_matching;

tests/unit/style/owning_handle.rs

@@ -0,0 +1,34 @@
+/* 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 owning_ref::RcRef;
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::sync::{Arc, RwLock};
+use style::owning_handle::OwningHandle;
+
+#[test]
+fn owning_handle() {
+    use std::cell::RefCell;
+    let cell = Rc::new(RefCell::new(2));
+    let cell_ref = RcRef::new(cell);
+    let mut handle = OwningHandle::new(cell_ref, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+    assert_eq!(*handle, 2);
+    *handle = 3;
+    assert_eq!(*handle, 3);
+}
+
+#[test]
+fn nested() {
+    let result = {
+        let complex = Rc::new(RefCell::new(Arc::new(RwLock::new("someString"))));
+        let curr = RcRef::new(complex);
+        let curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+        let mut curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().try_write().unwrap());
+        assert_eq!(*curr, "someString");
+        *curr = "someOtherString";
+        curr
+    };
+    assert_eq!(*result, "someOtherString");
+}