Reuse StylesheetContent for inline style sheets with identical content (#38540)

For duplicate style sheets with identical content, `StylesheetContents`
can be reused to avoid redundant parsing of the inline style sheets.
Since duplicate stylesheets is a common case with web components, this
change will significantly improve performance. Additionally, the cache
hit rate of stylo's `CascadeDataCache` can now be significantly
improved.

When shared `StylesheetContents` is modified, copy-on-write will occur
to avoid affecting other sharers. And then updates the references to
`CssRule` or `PropertyDeclarationBlock` stored in the CSSOMs to ensure
that modifications are made only on the new copy.

Signed-off-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>

components/script/dom/cssmediarule.rs

@@ -2,9 +2,11 @@
  * 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 std::cell::RefCell;
+
 use dom_struct::dom_struct;
 use servo_arc::Arc;
-use style::shared_lock::ToCssWithGuard;
+use style::shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
 use style::stylesheets::{CssRuleType, MediaRule};
 use style_traits::ToCss;
 
@@ -24,7 +26,7 @@ pub(crate) struct CSSMediaRule {
     cssconditionrule: CSSConditionRule,
     #[ignore_malloc_size_of = "Arc"]
     #[no_trace]
-    mediarule: Arc<MediaRule>,
+    mediarule: RefCell<Arc<MediaRule>>,
     medialist: MutNullableDom<MediaList>,
 }
 
@@ -33,7 +35,7 @@ impl CSSMediaRule {
         let list = mediarule.rules.clone();
         CSSMediaRule {
             cssconditionrule: CSSConditionRule::new_inherited(parent_stylesheet, list),
-            mediarule,
+            mediarule: RefCell::new(mediarule),
             medialist: MutNullableDom::new(None),
         }
     }
@@ -57,7 +59,7 @@ impl CSSMediaRule {
             MediaList::new(
                 self.global().as_window(),
                 self.cssconditionrule.parent_stylesheet(),
-                self.mediarule.media_queries.clone(),
+                self.mediarule.borrow().media_queries.clone(),
                 can_gc,
             )
         })
@@ -66,8 +68,21 @@ impl CSSMediaRule {
     /// <https://drafts.csswg.org/css-conditional-3/#the-cssmediarule-interface>
     pub(crate) fn get_condition_text(&self) -> DOMString {
         let guard = self.cssconditionrule.shared_lock().read();
-        let list = self.mediarule.media_queries.read_with(&guard);
-        list.to_css_string().into()
+        self.mediarule
+            .borrow()
+            .media_queries
+            .read_with(&guard)
+            .to_css_string()
+            .into()
+    }
+
+    pub(crate) fn update_rule(&self, mediarule: Arc<MediaRule>, guard: &SharedRwLockReadGuard) {
+        self.cssconditionrule
+            .update_rules(mediarule.rules.clone(), guard);
+        if let Some(medialist) = self.medialist.get() {
+            medialist.update_media_list(mediarule.media_queries.clone());
+        }
+        *self.mediarule.borrow_mut() = mediarule;
     }
 }
 
@@ -78,7 +93,7 @@ impl SpecificCSSRule for CSSMediaRule {
 
     fn get_css(&self) -> DOMString {
         let guard = self.cssconditionrule.shared_lock().read();
-        self.mediarule.to_css_string(&guard).into()
+        self.mediarule.borrow().to_css_string(&guard).into()
     }
 }