LibHTML: Introduce the HtmlView widget

This is a GWidget that can display contents of an HTML document.
It replaces the Frame class.

Libraries/LibHTML/HtmlView.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <LibGUI/GScrollableWidget.h>
+#include <LibHTML/DOM/Document.h>
+
+class HtmlView : public GScrollableWidget {
+    C_OBJECT(HtmlView)
+public:
+    virtual ~HtmlView() override {}
+
+    Document* document() { return m_document; }
+    const Document* document() const { return m_document; }
+    void set_document(Document*);
+
+protected:
+    HtmlView(GWidget* parent = nullptr);
+
+    virtual void resize_event(GResizeEvent&) override;
+    virtual void paint_event(GPaintEvent&) override;
+
+private:
+    void layout_and_sync_size();
+
+    RefPtr<Document> m_document;
+    RefPtr<LayoutNode> m_layout_root;
+};