LibWeb: Reimplement the <style> element following the spec

We now follow the "update a style block" algorithm from the HTML spec
instead of using the ad-hoc CSSLoader mechanism.

This necessitated improving our StyleSheet and CSSStyleSheet classes as
well, so that's baked into this commit.

Userland/Libraries/LibWeb/CSS/CSSStyleSheet.h

@@ -27,6 +27,8 @@ public:
 
     virtual ~CSSStyleSheet() override;
 
+    void set_owner_css_rule(CSSRule* rule) { m_owner_css_rule = rule; }
+
     virtual String type() const override { return "text/css"; }
 
     CSSRuleList const& rules() const { return m_rules; }
@@ -76,6 +78,9 @@ private:
     explicit CSSStyleSheet(NonnullRefPtrVector<CSSRule>);
 
     NonnullRefPtr<CSSRuleList> m_rules;
+
+    // FIXME: Use WeakPtr.
+    CSSRule* m_owner_css_rule { nullptr };
 };
 
 }

Userland/Libraries/LibWeb/CSS/StyleSheet.h

@@ -26,11 +26,39 @@ public:
     DOM::Element* owner_node() { return m_owner_node; }
     void set_owner_node(DOM::Element*);
 
+    String title() const { return m_title; }
+    void set_title(String title) { m_title = move(title); }
+
+    void set_type(String type) { m_type_string = move(type); }
+    void set_media(String media) { m_media_string = move(media); }
+
+    bool is_alternate() const { return m_alternate; }
+    void set_alternate(bool alternate) { m_alternate = alternate; }
+
+    void set_origin_clean(bool origin_clean) { m_origin_clean = origin_clean; }
+
+    bool disabled() const { return m_disabled; }
+    void set_disabled(bool disabled) { m_disabled = disabled; }
+
+    CSSStyleSheet* parent_style_sheet() { return m_parent_style_sheet; }
+    void set_parent_css_style_sheet(CSSStyleSheet* sheet) { m_parent_style_sheet = sheet; }
+
 protected:
     StyleSheet() = default;
 
 private:
     WeakPtr<DOM::Element> m_owner_node;
+
+    // FIXME: Use WeakPtr.
+    CSSStyleSheet* m_parent_style_sheet { nullptr };
+
+    String m_title;
+    String m_type_string;
+    String m_media_string;
+
+    bool m_disabled { false };
+    bool m_alternate { false };
+    bool m_origin_clean { true };
 };
 
 }

Userland/Libraries/LibWeb/CSS/StyleSheet.idl

@@ -4,9 +4,9 @@ interface StyleSheet {
     readonly attribute CSSOMString type;
 
     // readonly attribute USVString? href;
-    // readonly attribute CSSStyleSheet? parentStyleSheet;
-    // readonly attribute DOMString? title;
+    readonly attribute CSSStyleSheet? parentStyleSheet;
+    readonly attribute DOMString? title;
     // [SameObject, PutForwards=mediaText] readonly attribute MediaList media;
-    // attribute boolean disabled;
+    attribute boolean disabled;
 
 };

Userland/Libraries/LibWeb/CSS/StyleSheetList.cpp

@@ -10,9 +10,15 @@ namespace Web::CSS {
 
 void StyleSheetList::add_sheet(NonnullRefPtr<CSSStyleSheet> sheet)
 {
+    VERIFY(!m_sheets.contains_slow(sheet));
     m_sheets.append(move(sheet));
 }
 
+void StyleSheetList::remove_sheet(CSSStyleSheet& sheet)
+{
+    m_sheets.remove_first_matching([&](auto& entry) { return &*entry == &sheet; });
+}
+
 StyleSheetList::StyleSheetList(DOM::Document& document)
     : m_document(document)
 {

Userland/Libraries/LibWeb/CSS/StyleSheetList.h

@@ -26,6 +26,8 @@ public:
     }
 
     void add_sheet(NonnullRefPtr<CSSStyleSheet>);
+    void remove_sheet(CSSStyleSheet&);
+
     const NonnullRefPtrVector<CSSStyleSheet>& sheets() const { return m_sheets; }
 
     RefPtr<CSSStyleSheet> item(size_t index) const