Fix: Add support for stylesheet MIME type quirk in quirks mode (#36338)

This PR implements the HTML spec quirk for stylesheets:
https://html.spec.whatwg.org/multipage/#link-type-stylesheet

The implementation adds a check in `stylesheet_loader.rs` to handle this
quirk condition correctly, and adds a new WPT test to verify that
same-origin non-CSS MIME type resources are properly treated as CSS in
quirks mode.

Testing: Added a new WPT test (`quirk-origin-check-positive.html`) that
verifies the positive case for this quirk.
Fixes: https://github.com/servo/servo/issues/36324

---------

Signed-off-by: saku-1101 <sakupi1101@outlook.jp>

1 files changed, 11 insertions, 1 deletions

diff --git a/components/script/stylesheet_loader.rs b/components/script/stylesheet_loader.rs
index 6290d2709cc..7c7f7f98a07 100644
--- a/components/script/stylesheet_loader.rs
+++ b/components/script/stylesheet_loader.rs
@@ -15,6 +15,7 @@ use net_traits::{
 };
 use servo_arc::Arc;
 use servo_url::ServoUrl;
+use style::context::QuirksMode;
 use style::media_queries::MediaList;
 use style::parser::ParserContext;
 use style::shared_lock::{Locked, SharedRwLock};
@@ -164,7 +165,16 @@ impl FetchResponseListener for StylesheetContext {
             let is_css = metadata.content_type.is_some_and(|ct| {
                 let mime: Mime = ct.into_inner().into();
                 mime.type_() == mime::TEXT && mime.subtype() == mime::CSS
-            });
+            }) || (
+                // Quirk: If the document has been set to quirks mode,
+                // has the same origin as the URL of the external resource,
+                // and the Content-Type metadata of the external resource
+                // is not a supported style sheet type, the user agent must
+                // instead assume it to be text/css.
+                // <https://html.spec.whatwg.org/multipage/#link-type-stylesheet>
+                document.quirks_mode() == QuirksMode::Quirks &&
+                    document.origin().immutable().clone() == metadata.final_url.origin()
+            );
 
             let data = if is_css {
                 let data = std::mem::take(&mut self.data);