LibWeb: Don't load stylesheets with rel="alternate"

We're not supposed to load these by default. Alternate stylesheets can
be offered in a menu or something, if the user is interested.

Libraries/LibWeb/DOM/HTMLLinkElement.cpp

@@ -47,7 +47,7 @@ void HTMLLinkElement::inserted_into(Node& node)
 {
     HTMLElement::inserted_into(node);
 
-    if (rel().split_view(' ').contains_slow("stylesheet"))
+    if (m_relationship & Relationship::Stylesheet && !(m_relationship & Relationship::Alternate))
         load_stylesheet(document().complete_url(href()));
 }
 
@@ -87,4 +87,18 @@ void HTMLLinkElement::load_stylesheet(const URL& url)
     set_resource(ResourceLoader::the().load_resource(Resource::Type::Generic, request));
 }
 
+void HTMLLinkElement::parse_attribute(const FlyString& name, const String& value)
+{
+    if (name == HTML::AttributeNames::rel) {
+        m_relationship = 0;
+        auto parts = value.split_view(' ');
+        for (auto& part : parts) {
+            if (part == "stylesheet")
+                m_relationship |= Relationship::Stylesheet;
+            else if (part == "alternate")
+                m_relationship |= Relationship::Alternate;
+        }
+    }
+}
+
 }

Libraries/LibWeb/DOM/HTMLLinkElement.h

@@ -49,8 +49,18 @@ private:
     virtual void resource_did_fail() override;
     virtual void resource_did_load() override;
 
+    void parse_attribute(const FlyString&, const String&) override;
+
     void load_stylesheet(const URL&);
 
+    struct Relationship {
+        enum {
+            Alternate = 1 << 0,
+            Stylesheet = 1 << 1,
+        };
+    };
+
+    unsigned m_relationship { 0 };
     RefPtr<StyleSheet> m_style_sheet;
 };