LibDevTools: Stub out a layout inspector actor

The DevTools client will ask for this actor before trying to render any
box model or computed style information. We can just stub out this actor
for now.

Libraries/LibDevTools/Actors/LayoutInspectorActor.cpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/JsonArray.h>
+#include <AK/JsonObject.h>
+#include <LibDevTools/Actors/LayoutInspectorActor.h>
+
+namespace DevTools {
+
+NonnullRefPtr<LayoutInspectorActor> LayoutInspectorActor::create(DevToolsServer& devtools, String name)
+{
+    return adopt_ref(*new LayoutInspectorActor(devtools, move(name)));
+}
+
+LayoutInspectorActor::LayoutInspectorActor(DevToolsServer& devtools, String name)
+    : Actor(devtools, move(name))
+{
+}
+
+LayoutInspectorActor::~LayoutInspectorActor() = default;
+
+void LayoutInspectorActor::handle_message(StringView type, JsonObject const&)
+{
+    JsonObject response;
+    response.set("from"sv, name());
+
+    if (type == "getCurrentFlexbox"sv) {
+        response.set("flexbox"sv, JsonValue {});
+        send_message(move(response));
+        return;
+    }
+
+    if (type == "getGrids"sv) {
+        response.set("grids"sv, JsonArray {});
+        send_message(move(response));
+        return;
+    }
+
+    send_unrecognized_packet_type_error(type);
+}
+
+}

Libraries/LibDevTools/Actors/LayoutInspectorActor.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <LibDevTools/Actor.h>
+
+namespace DevTools {
+
+class LayoutInspectorActor final : public Actor {
+public:
+    static constexpr auto base_name = "layout-inspector"sv;
+
+    static NonnullRefPtr<LayoutInspectorActor> create(DevToolsServer&, String name);
+    virtual ~LayoutInspectorActor() override;
+
+    virtual void handle_message(StringView type, JsonObject const&) override;
+
+private:
+    LayoutInspectorActor(DevToolsServer&, String name);
+};
+
+}

Libraries/LibDevTools/Actors/WalkerActor.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/JsonArray.h>
 #include <AK/StringUtils.h>
+#include <LibDevTools/Actors/LayoutInspectorActor.h>
 #include <LibDevTools/Actors/NodeActor.h>
 #include <LibDevTools/Actors/TabActor.h>
 #include <LibDevTools/Actors/WalkerActor.h>
@@ -59,6 +60,18 @@ void WalkerActor::handle_message(StringView type, JsonObject const& message)
         return;
     }
 
+    if (type == "getLayoutInspector"sv) {
+        if (!m_layout_inspector)
+            m_layout_inspector = devtools().register_actor<LayoutInspectorActor>();
+
+        JsonObject actor;
+        actor.set("actor"sv, m_layout_inspector->name());
+
+        response.set("actor"sv, move(actor));
+        send_message(move(response));
+        return;
+    }
+
     if (type == "querySelector"sv) {
         auto node = message.get_string("node"sv);
         if (!node.has_value()) {

Libraries/LibDevTools/Actors/WalkerActor.h

@@ -44,6 +44,8 @@ private:
     void populate_dom_tree_cache(JsonObject& node, JsonObject const* parent = nullptr);
 
     WeakPtr<TabActor> m_tab;
+    WeakPtr<LayoutInspectorActor> m_layout_inspector;
+
     JsonObject m_dom_tree;
 
     HashMap<JsonObject const*, JsonObject const*> m_dom_node_to_parent_map;

Libraries/LibDevTools/CMakeLists.txt

@@ -5,6 +5,7 @@ set(SOURCES
     Actors/FrameActor.cpp
     Actors/HighlighterActor.cpp
     Actors/InspectorActor.cpp
+    Actors/LayoutInspectorActor.cpp
     Actors/NodeActor.cpp
     Actors/PageStyleActor.cpp
     Actors/PreferenceActor.cpp

Libraries/LibDevTools/Forward.h

@@ -17,6 +17,7 @@ class DevToolsServer;
 class FrameActor;
 class HighlighterActor;
 class InspectorActor;
+class LayoutInspectorActor;
 class NodeActor;
 class PageStyleActor;
 class PreferenceActor;