LibWeb: Process style sheets in document order

Until now we would simply apply stylesheets in the order they finished
loading. This patch adds a StyleSheetList object that hangs off of each
Document and contains all the style sheets in document order.

There's still a lot of work to do for a proper cascade, but at least
this makes us consistently wrong every time. :^)

Libraries/LibWeb/DOM/Document.cpp

@@ -63,6 +63,7 @@ namespace Web {
 Document::Document(const URL& url)
     : ParentNode(*this, NodeType::DOCUMENT_NODE)
     , m_style_resolver(make<StyleResolver>(*this))
+    , m_style_sheets(CSS::StyleSheetList::create(*this))
     , m_url(url)
     , m_window(Window::create_with_document(*this))
 {

Libraries/LibWeb/DOM/Document.h

@@ -37,6 +37,7 @@
 #include <LibJS/Forward.h>
 #include <LibWeb/CSS/StyleResolver.h>
 #include <LibWeb/CSS/StyleSheet.h>
+#include <LibWeb/CSS/StyleSheetList.h>
 #include <LibWeb/DOM/NonElementParentNode.h>
 #include <LibWeb/DOM/ParentNode.h>
 
@@ -63,8 +64,8 @@ public:
     StyleResolver& style_resolver() { return *m_style_resolver; }
     const StyleResolver& style_resolver() const { return *m_style_resolver; }
 
-    void add_sheet(const StyleSheet& sheet) { m_sheets.append(sheet); }
-    const NonnullRefPtrVector<StyleSheet>& stylesheets() const { return m_sheets; }
+    CSS::StyleSheetList& style_sheets() { return *m_style_sheets; }
+    const CSS::StyleSheetList& style_sheets() const { return *m_style_sheets; }
 
     virtual FlyString tag_name() const override { return "#document"; }
 
@@ -146,7 +147,7 @@ private:
     virtual RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const override;
 
     OwnPtr<StyleResolver> m_style_resolver;
-    NonnullRefPtrVector<StyleSheet> m_sheets;
+    RefPtr<CSS::StyleSheetList> m_style_sheets;
     RefPtr<Node> m_hovered_node;
     RefPtr<Node> m_inspected_node;
     WeakPtr<Frame> m_frame;

Libraries/LibWeb/DOM/HTMLLinkElement.cpp

@@ -68,12 +68,20 @@ void HTMLLinkElement::resource_did_load()
         dbg() << "HTMLLinkElement: Failed to parse stylesheet: " << href();
         return;
     }
-    document().add_sheet(*sheet);
+
+    // Transfer the rules from the successfully parsed sheet into the sheet we've already inserted.
+    m_style_sheet->rules() = sheet->rules();
+
     document().update_style();
 }
 
 void HTMLLinkElement::load_stylesheet(const URL& url)
 {
+    // First insert an empty style sheet in the document sheet list.
+    // There's probably a nicer way to do this, but this ensures that sheets are in document order.
+    m_style_sheet = StyleSheet::create({});
+    document().style_sheets().add_sheet(*m_style_sheet);
+
     LoadRequest request;
     request.set_url(url);
     set_resource(ResourceLoader::the().load_resource(Resource::Type::Generic, request));

Libraries/LibWeb/DOM/HTMLLinkElement.h

@@ -50,6 +50,8 @@ private:
     virtual void resource_did_load() override;
 
     void load_stylesheet(const URL&);
+
+    RefPtr<StyleSheet> m_style_sheet;
 };
 
 template<>

Libraries/LibWeb/DOM/HTMLStyleElement.cpp

@@ -50,7 +50,9 @@ void HTMLStyleElement::children_changed()
     });
     m_stylesheet = parse_css(builder.to_string());
     if (m_stylesheet)
-        document().add_sheet(*m_stylesheet);
+        document().style_sheets().add_sheet(*m_stylesheet);
+    else
+        document().style_sheets().add_sheet(StyleSheet::create({}));
     HTMLElement::children_changed();
 }