Eliminate duplicate Layout DOM wrappers

There are duplicate sets of Layout DOM wrappers: one for Layout 2013 and
one for Layout 2020. As part of cleaning up and simplifying the
wrappers, this change parameterizes them on the specific layout data
they contain. This allows them to be shared again. In addition, various
small cleanups are included.

Fixes #29691.

components/script/layout_dom/shadow_root.rs

@@ -0,0 +1,84 @@
+/* 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::LayoutDom;
+use crate::dom::shadowroot::{LayoutShadowRootHelpers, ShadowRoot};
+use crate::layout_dom::ServoLayoutElement;
+use crate::layout_dom::ServoLayoutNode;
+use script_layout_interface::wrapper_traits::LayoutDataTrait;
+use selectors::matching::QuirksMode;
+use std::fmt;
+use std::marker::PhantomData;
+use style::dom::TShadowRoot;
+use style::media_queries::Device;
+use style::shared_lock::SharedRwLockReadGuard as StyleSharedRwLockReadGuard;
+use style::stylist::CascadeData;
+
+pub struct ServoShadowRoot<'dom, LayoutDataType: LayoutDataTrait> {
+    /// The wrapped private DOM ShadowRoot.
+    shadow_root: LayoutDom<'dom, ShadowRoot>,
+
+    /// A PhantomData that is used to track the type of the stored layout data.
+    phantom: PhantomData<LayoutDataType>,
+}
+
+impl<'dom, LayoutDataType: LayoutDataTrait> Clone for ServoShadowRoot<'dom, LayoutDataType> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+impl<'dom, LayoutDataType: LayoutDataTrait> Copy for ServoShadowRoot<'dom, LayoutDataType> {}
+
+impl<'a, LayoutDataType: LayoutDataTrait> PartialEq for ServoShadowRoot<'a, LayoutDataType> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.shadow_root == other.shadow_root
+    }
+}
+
+impl<'dom, LayoutDataType: LayoutDataTrait> fmt::Debug for ServoShadowRoot<'dom, LayoutDataType> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.as_node().fmt(f)
+    }
+}
+
+impl<'dom, LayoutDataType: LayoutDataTrait> ::style::dom::TShadowRoot
+    for ServoShadowRoot<'dom, LayoutDataType>
+{
+    type ConcreteNode = ServoLayoutNode<'dom, LayoutDataType>;
+
+    fn as_node(&self) -> Self::ConcreteNode {
+        ServoLayoutNode::from_layout_js(self.shadow_root.upcast())
+    }
+
+    fn host(&self) -> ServoLayoutElement<'dom, LayoutDataType> {
+        ServoLayoutElement::from_layout_js(self.shadow_root.get_host_for_layout())
+    }
+
+    fn style_data<'a>(&self) -> Option<&'a CascadeData>
+    where
+        Self: 'a,
+    {
+        Some(&self.shadow_root.get_style_data_for_layout())
+    }
+}
+
+impl<'dom, LayoutDataType: LayoutDataTrait> ServoShadowRoot<'dom, LayoutDataType> {
+    pub(super) fn from_layout_js(shadow_root: LayoutDom<'dom, ShadowRoot>) -> Self {
+        ServoShadowRoot {
+            shadow_root,
+            phantom: PhantomData,
+        }
+    }
+
+    pub unsafe fn flush_stylesheets(
+        &self,
+        device: &Device,
+        quirks_mode: QuirksMode,
+        guard: &StyleSharedRwLockReadGuard,
+    ) {
+        self.shadow_root
+            .flush_stylesheets::<ServoLayoutElement<LayoutDataType>>(device, quirks_mode, guard)
+    }
+}