LibWeb: Rename LayoutNode classes and move them into Layout namespace

Bring the names of various boxes closer to spec language. This should
hopefully make things easier to understand and hack on. :^)

Some notable changes:

- LayoutNode -> Layout::Node
- LayoutBox -> Layout::Box
- LayoutBlock -> Layout::BlockBox
- LayoutReplaced -> Layout::ReplacedBox
- LayoutDocument -> Layout::InitialContainingBlockBox
- LayoutText -> Layout::TextNode
- LayoutInline -> Layout::InlineNode

Note that this is not strictly a "box tree" as we also hang inline/text
nodes in the same tree, and they don't generate boxes. (Instead, they
contribute line box fragments to their containing block!)

Libraries/LibWeb/Layout/FrameBox.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <LibWeb/HTML/HTMLIFrameElement.h>
+#include <LibWeb/Layout/ReplacedBox.h>
+
+namespace Web::Layout {
+
+class FrameBox final : public ReplacedBox {
+public:
+    FrameBox(DOM::Document&, DOM::Element&, NonnullRefPtr<CSS::StyleProperties>);
+    virtual ~FrameBox() override;
+
+    virtual void paint(PaintContext&, PaintPhase) override;
+    virtual void prepare_for_replaced_layout() override;
+
+    const HTML::HTMLIFrameElement& dom_node() const { return downcast<HTML::HTMLIFrameElement>(ReplacedBox::dom_node()); }
+    HTML::HTMLIFrameElement& dom_node() { return downcast<HTML::HTMLIFrameElement>(ReplacedBox::dom_node()); }
+
+private:
+    virtual bool is_frame() const final { return true; }
+    virtual const char* class_name() const override { return "FrameBox"; }
+    virtual void did_set_rect() override;
+};
+
+}
+
+AK_BEGIN_TYPE_TRAITS(Web::Layout::FrameBox)
+static bool is_type(const Web::Layout::Node& layout_node) { return layout_node.is_frame(); }
+AK_END_TYPE_TRAITS()