Browser+LibWeb+WebContent: Show style for pseudo-elements :^)

This expands the InspectorWidget::Selection to include an optional
PseudoElement, which is then passed over IPC to request style
information for it.

As noted, this has some pretty big limitations because pseudo-elements
don't have DOM nodes:
- Declared style has to be recalculated when it's requested.
- We don't display the computed style.
- We don't display custom properties.

Userland/Libraries/LibWeb/DOMTreeModel.cpp

@@ -182,22 +182,39 @@ void DOMTreeModel::map_dom_nodes_to_parent(JsonObject const* parent, JsonObject
     });
 }
 
-GUI::ModelIndex DOMTreeModel::index_for_node(i32 node_id) const
+GUI::ModelIndex DOMTreeModel::index_for_node(i32 node_id, Optional<Web::CSS::Selector::PseudoElement> pseudo_element) const
 {
     auto node = m_node_id_to_dom_node_map.get(node_id).value_or(nullptr);
     if (node) {
-        auto* parent = get_parent(*node);
-        if (!parent)
-            return {};
-        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);
+        if (pseudo_element.has_value()) {
+            // Find pseudo-element child of the node.
+            auto node_children = get_children(*node);
+            for (size_t i = 0; i < node_children->size(); i++) {
+                auto& child = node_children->at(i).as_object();
+                if (!child.has("pseudo-element"))
+                    continue;
+
+                auto child_pseudo_element = child.get("pseudo-element");
+                if (!child_pseudo_element.is_i32())
+                    continue;
+
+                if (child_pseudo_element.as_i32() == to_underlying(pseudo_element.value()))
+                    return create_index(i, 0, &child);
+            }
+        } else {
+            auto* parent = get_parent(*node);
+            if (!parent)
+                return {};
+            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);
+    dbgln("Didn't find index for node {}, pseudo-element {}!", node_id, pseudo_element.has_value() ? CSS::pseudo_element_name(pseudo_element.value()) : "NONE");
     return {};
 }
 

Userland/Libraries/LibWeb/DOMTreeModel.h

@@ -10,6 +10,7 @@
 #include <AK/HashMap.h>
 #include <AK/JsonObject.h>
 #include <LibGUI/Model.h>
+#include <LibWeb/CSS/Selector.h>
 #include <LibWeb/Forward.h>
 
 namespace Web {
@@ -30,7 +31,7 @@ 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;
+    GUI::ModelIndex index_for_node(i32 node_id, Optional<Web::CSS::Selector::PseudoElement> pseudo_element) const;
 
 private:
     DOMTreeModel(JsonObject, GUI::TreeView&);

Userland/Libraries/LibWeb/OutOfProcessWebView.cpp

@@ -439,9 +439,9 @@ void OutOfProcessWebView::inspect_dom_tree()
     client().async_inspect_dom_tree();
 }
 
-Optional<OutOfProcessWebView::DOMNodeProperties> OutOfProcessWebView::inspect_dom_node(i32 node_id)
+Optional<OutOfProcessWebView::DOMNodeProperties> OutOfProcessWebView::inspect_dom_node(i32 node_id, Optional<CSS::Selector::PseudoElement> pseudo_element)
 {
-    auto response = client().inspect_dom_node(node_id);
+    auto response = client().inspect_dom_node(node_id, pseudo_element);
     if (!response.has_style())
         return {};
     return DOMNodeProperties {
@@ -454,7 +454,7 @@ Optional<OutOfProcessWebView::DOMNodeProperties> OutOfProcessWebView::inspect_do
 
 void OutOfProcessWebView::clear_inspected_dom_node()
 {
-    client().inspect_dom_node(0);
+    client().inspect_dom_node(0, {});
 }
 
 i32 OutOfProcessWebView::get_hovered_node_id()

Userland/Libraries/LibWeb/OutOfProcessWebView.h

@@ -9,6 +9,7 @@
 #include <AK/URL.h>
 #include <LibGUI/AbstractScrollableWidget.h>
 #include <LibGUI/Widget.h>
+#include <LibWeb/CSS/Selector.h>
 #include <LibWeb/Page/Page.h>
 #include <LibWeb/WebViewHooks.h>
 
@@ -40,7 +41,7 @@ public:
         String custom_properties_json;
         String node_box_sizing_json;
     };
-    Optional<DOMNodeProperties> inspect_dom_node(i32 node_id);
+    Optional<DOMNodeProperties> inspect_dom_node(i32 node_id, Optional<CSS::Selector::PseudoElement>);
     void clear_inspected_dom_node();
     i32 get_hovered_node_id();