Add sugar for already_AddRefed and use it for conversion between Atom and nsIAtom pointer.

components/style/gecko_bindings/sugar/already_addrefed.rs

@@ -0,0 +1,48 @@
+/* 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/. */
+
+//! little helpers for `already_AddRefed`.
+
+use gecko_bindings::structs::already_AddRefed;
+use std::marker::PhantomData;
+use std::mem;
+
+impl<T> already_AddRefed<T> {
+    /// Create an already_AddRefed from an addrefed pointer.
+    #[inline]
+    pub unsafe fn new(ptr: *mut T) -> Option<Self> {
+        if !ptr.is_null() {
+            Some(Self::new_unchecked(ptr))
+        } else {
+            None
+        }
+    }
+
+    /// Create an already_AddRefed from an non-nullable addrefed pointer.
+    #[inline]
+    pub unsafe fn new_unchecked(ptr: *mut T) -> Self {
+        debug_assert!(!ptr.is_null());
+        already_AddRefed {
+            mRawPtr: ptr,
+            _phantom_0: PhantomData,
+        }
+    }
+
+    /// Take the addrefed pointer from this struct.
+    #[inline]
+    pub fn take(self) -> *mut T {
+        let ptr = self.mRawPtr;
+        mem::forget(self);
+        ptr
+    }
+}
+
+#[cfg(debug_assertions)]
+impl<T> Drop for already_AddRefed<T> {
+    fn drop(&mut self) {
+        // We really should instead mark already_AddRefed must_use, but
+        // we cannot currently, which is servo/rust-bindgen#710.
+        unreachable!("Destructor shouldn't be called, otherwise we are leaking")
+    }
+}

components/style/gecko_bindings/sugar/mod.rs

@@ -4,6 +4,7 @@
 
 //! Rust sugar and convenience methods for Gecko types.
 
+mod already_addrefed;
 mod ns_com_ptr;
 mod ns_compatibility;
 mod ns_css_shadow_array;

components/style/gecko_bindings/sugar/ns_css_value.rs

@@ -152,7 +152,7 @@ impl nsCSSValue {
 
     /// Set to an atom identifier value
     pub fn set_atom_ident(&mut self, s: Atom) {
-        unsafe { bindings::Gecko_CSSValue_SetAtomIdent(self, s.into_addrefed()) }
+        unsafe { bindings::Gecko_CSSValue_SetAtomIdent(self, s.into()) }
     }
 
     /// Set to a font format