Auto merge of #29873 - Loirooriol:import-assert, r=mrobinson

Avoid assert failure when using @import

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---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #29872

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because they only affect debug builds, and tests run in release builds.

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components/script/dom/htmlmetaelement.rs

@@ -114,7 +114,7 @@ impl HTMLMetaElement {
                     let shared_lock = document.style_shared_lock();
                     let rule = CssRule::Viewport(Arc::new(shared_lock.wrap(translated_rule)));
                     let sheet = Arc::new(Stylesheet {
-                        contents: StylesheetContents::from_shared_data(
+                        contents: StylesheetContents::from_data(
                             CssRules::new(vec![rule], shared_lock),
                             Origin::Author,
                             window_from_node(self).get_url(),

components/script/stylesheet_loader.rs

@@ -361,7 +361,7 @@ impl<'a> StyleStylesheetLoader for StylesheetLoader<'a> {
         layer: Option<ImportLayer>,
     ) -> Arc<Locked<ImportRule>> {
         let sheet = Arc::new(Stylesheet {
-            contents: StylesheetContents::from_shared_data(
+            contents: StylesheetContents::from_data(
                 CssRules::new(Vec::new(), lock),
                 context.stylesheet_origin,
                 context.url_data.clone(),

components/style/stylesheets/stylesheet.rs

@@ -125,13 +125,12 @@ impl StylesheetContents {
     /// An empty namespace map should be fine, as it is only used for parsing,
     /// not serialization of existing selectors.  Since UA sheets are read only,
     /// we should never need the namespace map.
-    pub fn from_shared_data(
+    pub fn from_data(
         rules: Arc<Locked<CssRules>>,
         origin: Origin,
         url_data: UrlExtraData,
         quirks_mode: QuirksMode,
     ) -> Arc<Self> {
-        debug_assert!(rules.is_static());
         Arc::new(Self {
             rules,
             origin,
@@ -144,6 +143,17 @@ impl StylesheetContents {
         })
     }
 
+    /// Same as above, but ensuring that the rules are static.
+    pub fn from_shared_data(
+        rules: Arc<Locked<CssRules>>,
+        origin: Origin,
+        url_data: UrlExtraData,
+        quirks_mode: QuirksMode,
+    ) -> Arc<Self> {
+        debug_assert!(rules.is_static());
+        Self::from_data(rules, origin, url_data, quirks_mode)
+    }
+
     /// Returns a reference to the list of rules.
     #[inline]
     pub fn rules<'a, 'b: 'a>(&'a self, guard: &'b SharedRwLockReadGuard) -> &'a [CssRule] {