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.cpp

@@ -0,0 +1,80 @@
+#include <LibGUI/GPainter.h>
+#include <LibGUI/GScrollBar.h>
+#include <LibHTML/Dump.h>
+#include <LibHTML/HtmlView.h>
+#include <LibHTML/Layout/LayoutNode.h>
+#include <LibHTML/RenderingContext.h>
+#include <stdio.h>
+
+HtmlView::HtmlView(GWidget* parent)
+    : GScrollableWidget(parent)
+{
+    set_frame_shape(FrameShape::Container);
+    set_frame_shadow(FrameShadow::Sunken);
+    set_frame_thickness(2);
+    set_should_hide_unnecessary_scrollbars(true);
+    set_background_color(Color::White);
+}
+
+void HtmlView::set_document(Document* document)
+{
+    if (document == m_document)
+        return;
+    m_document = document;
+
+    if (document == nullptr)
+        m_layout_root = nullptr;
+    else
+        m_layout_root = document->create_layout_tree(document->style_resolver(), nullptr);
+
+#ifdef HTML_DEBUG
+    if (document != nullptr) {
+        printf("\033[33;1mLayout tree before layout:\033[0m\n");
+        ::dump_tree(*m_layout_root);
+    }
+#endif
+
+    layout_and_sync_size();
+    update();
+}
+
+void HtmlView::layout_and_sync_size()
+{
+    if (!m_layout_root)
+        return;
+
+    m_layout_root->style().size().set_width(available_size().width());
+    m_layout_root->layout();
+    set_content_size(m_layout_root->rect().size());
+
+#ifdef HTML_DEBUG
+    printf("\033[33;1mLayout tree after layout:\033[0m\n");
+    ::dump_tree(*m_layout_root);
+#endif
+}
+
+void HtmlView::resize_event(GResizeEvent& event)
+{
+    GScrollableWidget::resize_event(event);
+    layout_and_sync_size();
+}
+
+void HtmlView::paint_event(GPaintEvent& event)
+{
+    GFrame::paint_event(event);
+
+    GPainter painter(*this);
+    painter.add_clip_rect(widget_inner_rect());
+    painter.add_clip_rect(event.rect());
+
+    painter.fill_rect(event.rect(), background_color());
+
+    painter.translate(frame_thickness(), frame_thickness());
+    painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+
+    if (!m_layout_root)
+        return;
+
+    RenderingContext context { painter };
+    m_layout_root->render(context);
+}