Introduce NodeRareData and ElementRareData

components/script/dom/raredata.rs

@@ -0,0 +1,24 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::dom::bindings::root::MutNullableDom;
+use crate::dom::shadowroot::ShadowRoot;
+
+#[derive(Default, JSTraceable, MallocSizeOf)]
+#[must_root]
+pub struct NodeRareData {
+    /// The shadow root the node belongs to.
+    /// This is None if the node is not in a shadow tree or
+    /// if it is a ShadowRoot.
+    pub owner_shadow_root: MutNullableDom<ShadowRoot>,
+}
+
+#[derive(Default, JSTraceable, MallocSizeOf)]
+#[must_root]
+pub struct ElementRareData {
+    /// https://dom.spec.whatwg.org/#dom-element-shadowroot
+    /// XXX This is currently not exposed to web content. Only for
+    ///     internal use.
+    pub shadow_root: MutNullableDom<ShadowRoot>,
+}