LibWeb: Render SVG-as-image into an isolated top-level browsing context

In order to separate the SVG content from the rest of the engine, it
gets its very own Page, PageClient, top-level browsing context, etc.

Unfortunately, we do have to get the palette and CSS/device pixel ratios
from the host Page for now, maybe that's something we could refactor in
the future.

Note that this doesn't work visually yet, since we don't calculate the
intrinsic sizes & ratio for SVG images. That comes next. :^)

Userland/Libraries/LibWeb/SVG/SVGDecodedImageData.cpp

@@ -5,24 +5,114 @@
  */
 
 #include <LibGfx/Bitmap.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/Dump.h>
+#include <LibWeb/Fetch/Infrastructure/HTTP/Responses.h>
+#include <LibWeb/HTML/BrowsingContext.h>
+#include <LibWeb/HTML/NavigationParams.h>
+#include <LibWeb/HTML/Parser/HTMLParser.h>
+#include <LibWeb/Layout/Viewport.h>
+#include <LibWeb/Painting/PaintContext.h>
 #include <LibWeb/SVG/SVGDecodedImageData.h>
+#include <LibWeb/SVG/SVGSVGElement.h>
 
 namespace Web::SVG {
 
-ErrorOr<NonnullRefPtr<SVGDecodedImageData>> SVGDecodedImageData::create(ByteBuffer)
+class SVGDecodedImageData::SVGPageClient final : public PageClient {
+public:
+    explicit SVGPageClient(Page& host_page)
+        : m_host_page(host_page)
+    {
+    }
+
+    virtual ~SVGPageClient() override = default;
+
+    Page& m_host_page;
+    Page* m_svg_page { nullptr };
+
+    virtual Page& page() override { return *m_svg_page; }
+    virtual Page const& page() const override { return *m_svg_page; }
+    virtual bool is_connection_open() const override { return false; }
+    virtual Gfx::Palette palette() const override { return m_host_page.client().palette(); }
+    virtual DevicePixelRect screen_rect() const override { return {}; }
+    virtual float device_pixels_per_css_pixel() const override { return m_host_page.client().device_pixels_per_css_pixel(); }
+    virtual CSS::PreferredColorScheme preferred_color_scheme() const override { return m_host_page.client().preferred_color_scheme(); }
+    virtual void request_file(FileRequest) override { }
+    virtual void paint(DevicePixelRect const&, Gfx::Bitmap&) override { }
+};
+
+ErrorOr<NonnullRefPtr<SVGDecodedImageData>> SVGDecodedImageData::create(Page& host_page, AK::URL const& url, ByteBuffer data)
 {
-    return adopt_nonnull_ref_or_enomem(new (nothrow) SVGDecodedImageData());
+    auto page_client = make<SVGPageClient>(host_page);
+    auto page = make<Page>(*page_client);
+    page_client->m_svg_page = page.ptr();
+    auto browsing_context = HTML::BrowsingContext::create_a_new_top_level_browsing_context(*page);
+    auto response = Fetch::Infrastructure::Response::create(browsing_context->vm());
+    response->url_list().append(url);
+    HTML::NavigationParams navigation_params {
+        .id = {},
+        .request = nullptr,
+        .response = response,
+        .origin = HTML::Origin {},
+        .policy_container = HTML::PolicyContainer {},
+        .final_sandboxing_flag_set = HTML::SandboxingFlagSet {},
+        .cross_origin_opener_policy = HTML::CrossOriginOpenerPolicy {},
+        .coop_enforcement_result = HTML::CrossOriginOpenerPolicyEnforcementResult {},
+        .reserved_environment = {},
+        .browsing_context = browsing_context,
+        .navigable = nullptr,
+    };
+    auto document = DOM::Document::create_and_initialize(DOM::Document::Type::HTML, "text/html", move(navigation_params)).release_value_but_fixme_should_propagate_errors();
+    browsing_context->set_active_document(document);
+
+    auto parser = HTML::HTMLParser::create_with_uncertain_encoding(document, data);
+    parser->run(document->url());
+
+    // Perform some DOM surgery to make the SVG root element be the first child of the Document.
+    // FIXME: This is a huge hack until we figure out how to actually parse separate SVG files.
+    auto* svg_root = document->body()->first_child_of_type<SVG::SVGSVGElement>();
+    svg_root->remove();
+    document->remove_all_children();
+
+    MUST(document->append_child(*svg_root));
+
+    return adopt_nonnull_ref_or_enomem(new (nothrow) SVGDecodedImageData(move(page), move(page_client), move(document), move(svg_root)));
 }
 
-SVGDecodedImageData::SVGDecodedImageData()
+SVGDecodedImageData::SVGDecodedImageData(NonnullOwnPtr<Page> page, NonnullOwnPtr<SVGPageClient> page_client, JS::Handle<DOM::Document> document, JS::Handle<SVG::SVGSVGElement> root_element)
+    : m_page(move(page))
+    , m_page_client(move(page_client))
+    , m_document(move(document))
+    , m_root_element(move(root_element))
 {
 }
 
 SVGDecodedImageData::~SVGDecodedImageData() = default;
 
-RefPtr<Gfx::Bitmap const> SVGDecodedImageData::bitmap(size_t, Gfx::IntSize) const
+void SVGDecodedImageData::render(Gfx::IntSize size) const
 {
-    return nullptr;
+    m_document->browsing_context()->set_viewport_rect({ 0, 0, size.width(), size.height() });
+    m_document->update_layout();
+
+    dump_tree(*m_document->layout_node());
+
+    Gfx::Painter painter(*m_bitmap);
+    PaintContext context(painter, m_page_client->palette(), m_page_client->device_pixels_per_css_pixel());
+
+    m_document->layout_node()->paint_all_phases(context);
+}
+
+RefPtr<Gfx::Bitmap const> SVGDecodedImageData::bitmap(size_t, Gfx::IntSize size) const
+{
+    if (size.is_empty())
+        return nullptr;
+
+    if (m_bitmap && m_bitmap->size() == size)
+        return m_bitmap;
+
+    m_bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::BGRA8888, size).release_value_but_fixme_should_propagate_errors();
+    render(size);
+    return m_bitmap;
 }
 
 Optional<CSSPixels> SVGDecodedImageData::intrinsic_width() const