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/csskeyframesrule.rs

@@ -2,10 +2,12 @@
  * 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 cssparser::{Parser, ParserInput};
 use dom_struct::dom_struct;
 use servo_arc::Arc;
-use style::shared_lock::{Locked, ToCssWithGuard};
+use style::shared_lock::{Locked, SharedRwLockReadGuard, ToCssWithGuard};
 use style::stylesheets::CssRuleType;
 use style::stylesheets::keyframes_rule::{Keyframe, KeyframeSelector, KeyframesRule};
 use style::values::KeyframesName;
@@ -28,7 +30,7 @@ pub(crate) struct CSSKeyframesRule {
     cssrule: CSSRule,
     #[ignore_malloc_size_of = "Arc"]
     #[no_trace]
-    keyframesrule: Arc<Locked<KeyframesRule>>,
+    keyframesrule: RefCell<Arc<Locked<KeyframesRule>>>,
     rulelist: MutNullableDom<CSSRuleList>,
 }
 
@@ -39,7 +41,7 @@ impl CSSKeyframesRule {
     ) -> CSSKeyframesRule {
         CSSKeyframesRule {
             cssrule: CSSRule::new_inherited(parent_stylesheet),
-            keyframesrule,
+            keyframesrule: RefCell::new(keyframesrule),
             rulelist: MutNullableDom::new(None),
         }
     }
@@ -67,7 +69,7 @@ impl CSSKeyframesRule {
             CSSRuleList::new(
                 self.global().as_window(),
                 parent_stylesheet,
-                RulesSource::Keyframes(self.keyframesrule.clone()),
+                RulesSource::Keyframes(self.keyframesrule.borrow().clone()),
                 can_gc,
             )
         })
@@ -82,6 +84,7 @@ impl CSSKeyframesRule {
             // This finds the *last* element matching a selector
             // because that's the rule that applies. Thus, rposition
             self.keyframesrule
+                .borrow()
                 .read_with(&guard)
                 .keyframes
                 .iter()
@@ -90,6 +93,18 @@ impl CSSKeyframesRule {
             None
         }
     }
+
+    pub(crate) fn update_rule(
+        &self,
+        keyframesrule: Arc<Locked<KeyframesRule>>,
+        guard: &SharedRwLockReadGuard,
+    ) {
+        if let Some(rulelist) = self.rulelist.get() {
+            rulelist.update_rules(RulesSource::Keyframes(keyframesrule.clone()), guard);
+        }
+
+        *self.keyframesrule.borrow_mut() = keyframesrule;
+    }
 }
 
 impl CSSKeyframesRuleMethods<crate::DomTypeHolder> for CSSKeyframesRule {
@@ -108,8 +123,10 @@ impl CSSKeyframesRuleMethods<crate::DomTypeHolder> for CSSKeyframesRule {
         );
 
         if let Ok(rule) = rule {
+            self.cssrule.parent_stylesheet().will_modify();
             let mut guard = self.cssrule.shared_lock().write();
             self.keyframesrule
+                .borrow()
                 .write_with(&mut guard)
                 .keyframes
                 .push(rule);
@@ -135,7 +152,7 @@ impl CSSKeyframesRuleMethods<crate::DomTypeHolder> for CSSKeyframesRule {
     // https://drafts.csswg.org/css-animations/#dom-csskeyframesrule-name
     fn Name(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
-        DOMString::from(&**self.keyframesrule.read_with(&guard).name.as_atom())
+        DOMString::from(&**self.keyframesrule.borrow().read_with(&guard).name.as_atom())
     }
 
     // https://drafts.csswg.org/css-animations/#dom-csskeyframesrule-name
@@ -143,9 +160,10 @@ impl CSSKeyframesRuleMethods<crate::DomTypeHolder> for CSSKeyframesRule {
         // Spec deviation: https://github.com/w3c/csswg-drafts/issues/801
         // Setting this property to a CSS-wide keyword or `none` does not throw,
         // it stores a value that serializes as a quoted string.
+        self.cssrule.parent_stylesheet().will_modify();
         let name = KeyframesName::from_ident(&value);
         let mut guard = self.cssrule.shared_lock().write();
-        self.keyframesrule.write_with(&mut guard).name = name;
+        self.keyframesrule.borrow().write_with(&mut guard).name = name;
         self.cssrule.parent_stylesheet().notify_invalidations();
         Ok(())
     }
@@ -159,6 +177,7 @@ impl SpecificCSSRule for CSSKeyframesRule {
     fn get_css(&self) -> DOMString {
         let guard = self.cssrule.shared_lock().read();
         self.keyframesrule
+            .borrow()
             .read_with(&guard)
             .to_css_string(&guard)
             .into()