LibDevTools: Add a helper to extract a DOM node JSON object more easily

The pattern of:

    auto tab = get_tab();
    auto walker = get_walker();

    if (tab && walker) {
        if (auto node = walker->dom_node(node_id)) {
            delegate().do_something(tab->description(), node);
        }
    }

Is getting a bit unergonomic and is often repeated. This patch just adds
a helper to WalkerActor to do most of this work, so now we have:

    if (auto node = WalkerActor::dom_node_for(get_walker(), node_id)) {
        delegate().do_something(node->tab->description(), node);
    }

Libraries/LibDevTools/Actors/HighlighterActor.cpp

@@ -39,15 +39,11 @@ void HighlighterActor::handle_message(StringView type, JsonObject const& message
             return;
         }
 
-        auto tab = InspectorActor::tab_for(m_inspector);
-        auto walker = InspectorActor::walker_for(m_inspector);
         response.set("value"sv, false);
 
-        if (tab && walker) {
-            if (auto const& dom_node = walker->dom_node(*node); dom_node.has_value()) {
-                devtools().delegate().highlight_dom_node(tab->description(), dom_node->id, dom_node->pseudo_element);
-                response.set("value"sv, true);
-            }
+        if (auto dom_node = WalkerActor::dom_node_for(InspectorActor::walker_for(m_inspector), *node); dom_node.has_value()) {
+            devtools().delegate().highlight_dom_node(dom_node->tab->description(), dom_node->id, dom_node->pseudo_element);
+            response.set("value"sv, true);
         }
 
         send_message(move(response));

Libraries/LibDevTools/Actors/NodeActor.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/JsonObject.h>
 #include <LibDevTools/Actors/NodeActor.h>
+#include <LibDevTools/Actors/TabActor.h>
 #include <LibDevTools/Actors/WalkerActor.h>
 
 namespace DevTools {
@@ -29,10 +30,8 @@ void NodeActor::handle_message(StringView type, JsonObject const&)
     response.set("from"sv, name());
 
     if (type == "getUniqueSelector"sv) {
-        if (auto walker = m_walker.strong_ref()) {
-            if (auto const& dom_node = walker->dom_node(name()); dom_node.has_value())
-                response.set("value"sv, dom_node->node.get_string("name"sv)->to_ascii_lowercase());
-        }
+        if (auto dom_node = WalkerActor::dom_node_for(m_walker, name()); dom_node.has_value())
+            response.set("value"sv, dom_node->node.get_string("name"sv)->to_ascii_lowercase());
 
         send_message(move(response));
         return;

Libraries/LibDevTools/Actors/PageStyleActor.cpp

@@ -95,19 +95,14 @@ JsonValue PageStyleActor::serialize_style() const
 template<typename Callback>
 void PageStyleActor::inspect_dom_node(StringView node_actor, Callback&& callback)
 {
-    auto tab = InspectorActor::tab_for(m_inspector);
-    auto walker = InspectorActor::walker_for(m_inspector);
-    if (!tab || !walker)
-        return;
-
-    auto const& dom_node = walker->dom_node(node_actor);
+    auto dom_node = WalkerActor::dom_node_for(InspectorActor::walker_for(m_inspector), node_actor);
     if (!dom_node.has_value())
         return;
 
     auto block_token = block_responses();
 
     devtools().delegate().inspect_dom_node(
-        tab->description(), dom_node->id, dom_node->pseudo_element,
+        dom_node->tab->description(), dom_node->id, dom_node->pseudo_element,
         [weak_self = make_weak_ptr<PageStyleActor>(), block_token = move(block_token), callback = forward<Callback>(callback)](ErrorOr<DOMNodeProperties> properties) mutable {
             if (properties.is_error()) {
                 dbgln_if(DEVTOOLS_DEBUG, "Unable to inspect DOM node: {}", properties.error());

Libraries/LibDevTools/Actors/WalkerActor.cpp

@@ -249,8 +249,19 @@ JsonValue WalkerActor::serialize_node(JsonObject const& node) const
     return serialized;
 }
 
+Optional<WalkerActor::DOMNode> WalkerActor::dom_node_for(WeakPtr<WalkerActor> const& weak_walker, StringView actor)
+{
+    if (auto walker = weak_walker.strong_ref())
+        return walker->dom_node(actor);
+    return {};
+}
+
 Optional<WalkerActor::DOMNode> WalkerActor::dom_node(StringView actor)
 {
+    auto tab = m_tab.strong_ref();
+    if (!tab)
+        return {};
+
     auto maybe_dom_node = m_actor_to_dom_node_map.get(actor);
     if (!maybe_dom_node.has_value() || !maybe_dom_node.value())
         return {};
@@ -268,7 +279,7 @@ Optional<WalkerActor::DOMNode> WalkerActor::dom_node(StringView actor)
     else
         node_id = dom_node.get_integer<Web::UniqueNodeID::Type>("id"sv).value();
 
-    return DOMNode { .node = dom_node, .id = node_id, .pseudo_element = pseudo_element };
+    return DOMNode { .node = dom_node, .id = node_id, .pseudo_element = pseudo_element, .tab = tab.release_nonnull() };
 }
 
 Optional<JsonObject const&> WalkerActor::find_node_by_selector(JsonObject const& node, StringView selector)

Libraries/LibDevTools/Actors/WalkerActor.h

@@ -32,7 +32,9 @@ public:
         JsonObject const& node;
         Web::UniqueNodeID id { 0 };
         Optional<Web::CSS::Selector::PseudoElement::Type> pseudo_element;
+        NonnullRefPtr<TabActor> tab;
     };
+    static Optional<DOMNode> dom_node_for(WeakPtr<WalkerActor> const&, StringView actor);
     Optional<DOMNode> dom_node(StringView actor);
 
 private: