stylo: Store servo computed values for animation properties

MozReview-Commit-ID: IoQLN5tdIBw

components/style/gecko_bindings/sugar/refptr.rs

@@ -5,10 +5,12 @@
 //! A rust helper to ease the use of Gecko's refcounted types.
 
 use gecko_bindings::structs;
+use gecko_bindings::sugar::ownership::HasArcFFI;
 use heapsize::HeapSizeOf;
 use std::{mem, ptr};
 use std::marker::PhantomData;
 use std::ops::{Deref, DerefMut};
+use std::sync::Arc;
 
 /// Trait for all objects that have Addref() and Release
 /// methods and can be placed inside RefPtr<T>
@@ -196,6 +198,14 @@ impl<T: RefCounted> structs::RefPtr<T> {
     }
 }
 
+impl<T> structs::RefPtr<T> {
+    /// Sets the contents to an Arc<T>
+    /// will leak existing contents
+    pub fn set_arc_leaky<U>(&mut self, other: Arc<U>) where U: HasArcFFI<FFIType = T> {
+        *self = unsafe { mem::transmute(other) }; // Arc::into_raw is unstable :(
+    }
+}
+
 impl<T: RefCounted> Drop for RefPtr<T> {
     fn drop(&mut self) {
         unsafe { self.release() }