LibWeb: Implement DOMTreeModel::index_for_node()

This will be used to find the index to select when the DOM Inspector is
told to inspect a specific node.

Userland/Libraries/LibWeb/DOMTreeModel.cpp

@@ -155,6 +155,7 @@ GUI::Variant DOMTreeModel::data(const GUI::ModelIndex& index, GUI::ModelRole rol
 void DOMTreeModel::map_dom_nodes_to_parent(JsonObject const* parent, JsonObject const* node)
 {
     m_dom_node_to_parent_map.set(node, parent);
+    m_node_id_to_dom_node_map.set(node->get("id").to_i32(), node);
 
     auto const* children = get_children(*node);
     if (!children)
@@ -166,4 +167,21 @@ void DOMTreeModel::map_dom_nodes_to_parent(JsonObject const* parent, JsonObject
     });
 }
 
+GUI::ModelIndex DOMTreeModel::index_for_node(i32 node_id) const
+{
+    auto node = m_node_id_to_dom_node_map.get(node_id).value_or(nullptr);
+    if (node) {
+        auto* parent = get_parent(*node);
+        auto parent_children = get_children(*parent);
+        for (size_t i = 0; i < parent_children->size(); i++) {
+            if (&parent_children->at(i).as_object() == node) {
+                return create_index(i, 0, node);
+            }
+        }
+    }
+
+    dbgln("Didn't find index for node {}!", node_id);
+    return {};
+}
+
 }

Userland/Libraries/LibWeb/DOMTreeModel.h

@@ -33,6 +33,8 @@ public:
     virtual GUI::ModelIndex index(int row, int column, const GUI::ModelIndex& parent = GUI::ModelIndex()) const override;
     virtual GUI::ModelIndex parent_index(const GUI::ModelIndex&) const override;
 
+    GUI::ModelIndex index_for_node(i32 node_id) const;
+
 private:
     explicit DOMTreeModel(JsonObject);
 
@@ -57,6 +59,7 @@ private:
     GUI::Icon m_text_icon;
     JsonObject m_dom_tree;
     HashMap<JsonObject const*, JsonObject const*> m_dom_node_to_parent_map;
+    HashMap<i32, JsonObject const*> m_node_id_to_dom_node_map;
 };
 
 }