style: Use ArcSlice for quotes.

This saves the intermediate allocation.

Differential Revision: https://phabricator.services.mozilla.com/D30546

components/style_traits/lib.rs

@@ -93,6 +93,7 @@ pub mod values;
 #[macro_use]
 pub mod viewport;
 pub mod owned_slice;
+pub mod owned_str;
 
 pub use crate::specified_value_info::{CssType, KeywordsCollectFn, SpecifiedValueInfo};
 pub use crate::values::{

components/style_traits/owned_str.rs

@@ -0,0 +1,53 @@
+/* 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/. */
+
+#![allow(unsafe_code)]
+
+//! A replacement for `Box<str>` that has a defined layout for FFI.
+
+use crate::owned_slice::OwnedSlice;
+use std::fmt;
+use std::ops::{Deref, DerefMut};
+
+/// A struct that basically replaces a Box<str>, but with a defined layout,
+/// suitable for FFI.
+#[repr(C)]
+#[derive(Default, Clone, PartialEq, Eq, MallocSizeOf, ToShmem)]
+pub struct OwnedStr(OwnedSlice<u8>);
+
+impl fmt::Debug for OwnedStr {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        self.deref().fmt(formatter)
+    }
+}
+
+impl Deref for OwnedStr {
+    type Target = str;
+
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        unsafe { std::str::from_utf8_unchecked(&*self.0) }
+    }
+}
+
+impl DerefMut for OwnedStr {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { std::str::from_utf8_unchecked_mut(&mut *self.0) }
+    }
+}
+
+impl From<Box<str>> for OwnedStr {
+    #[inline]
+    fn from(b: Box<str>) -> Self {
+        Self::from(b.into_string())
+    }
+}
+
+impl From<String> for OwnedStr {
+    #[inline]
+    fn from(s: String) -> Self {
+        OwnedStr(s.into_bytes().into())
+    }
+}

components/style_traits/specified_value_info.rs

@@ -84,6 +84,7 @@ impl SpecifiedValueInfo for u16 {}
 impl SpecifiedValueInfo for u32 {}
 impl SpecifiedValueInfo for str {}
 impl SpecifiedValueInfo for String {}
+impl SpecifiedValueInfo for crate::owned_str::OwnedStr {}
 
 #[cfg(feature = "servo")]
 impl SpecifiedValueInfo for ::servo_atoms::Atom {}

components/style_traits/values.rs

@@ -75,6 +75,16 @@ where
     }
 }
 
+impl ToCss for crate::owned_str::OwnedStr {
+    #[inline]
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        serialize_string(self, dest)
+    }
+}
+
 impl ToCss for str {
     #[inline]
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result