WebContent+Friends: Add IPC and plumbing for WebDriver endpoint

To use the `GET /session/{id}/element/{id}/css/{property name}`
WebDriver endpoint, two new IPC calls through the Browser are
implemented:
    - get_active_documents_type returns the type of the active document,
      which is either "xml" or "html"
    - get_computed_value_for_element returns the computed CSS value (as
      String) for the given element and CSS property name

Userland/Applications/Browser/BrowserWindow.cpp

@@ -598,6 +598,14 @@ void BrowserWindow::create_new_tab(URL url, bool activate)
         return active_tab().view().get_element_property(element_id, name);
     };
 
+    new_tab.on_get_active_documents_type = [this]() {
+        return active_tab().view().get_active_documents_type();
+    };
+
+    new_tab.on_get_computed_value_for_element = [this](i32 element_id, String const& property_name) {
+        return active_tab().view().get_computed_value_for_element(element_id, property_name);
+    };
+
     new_tab.load(url);
 
     dbgln_if(SPAM_DEBUG, "Added new tab {:p}, loading {}", &new_tab, url);

Userland/Applications/Browser/Tab.h

@@ -72,6 +72,8 @@ public:
     Function<Optional<Vector<i32>>(i32 start_node_id, String const&)> on_query_selector_all;
     Function<Optional<String>(i32 element_id, String const&)> on_get_element_attribute;
     Function<Optional<String>(i32 element_id, String const&)> on_get_element_property;
+    Function<String()> on_get_active_documents_type;
+    Function<String(i32 element_id, String const&)> on_get_computed_value_for_element;
 
     enum class InspectorTarget {
         Document,

Userland/Libraries/LibWebView/OutOfProcessWebView.cpp

@@ -535,6 +535,16 @@ Optional<String> OutOfProcessWebView::get_element_property(i32 element_id, Strin
     return client().get_element_property(element_id, name);
 }
 
+String OutOfProcessWebView::get_active_documents_type()
+{
+    return client().get_active_documents_type();
+}
+
+String OutOfProcessWebView::get_computed_value_for_element(i32 element_id, String const& property_name)
+{
+    return client().get_computed_value_for_element(element_id, property_name);
+}
+
 void OutOfProcessWebView::set_content_filters(Vector<String> filters)
 {
     client().async_set_content_filters(filters);

Userland/Libraries/LibWebView/OutOfProcessWebView.h

@@ -62,6 +62,8 @@ public:
     Optional<Vector<i32>> query_selector_all(i32 start_node_id, String const& selector);
     Optional<String> get_element_attribute(i32 element_id, String const& name);
     Optional<String> get_element_property(i32 element_id, String const& name);
+    String get_active_documents_type();
+    String get_computed_value_for_element(i32 element_id, String const& property_name);
 
     void set_content_filters(Vector<String>);
     void set_proxy_mappings(Vector<String> proxies, HashMap<String, size_t> mappings);

Userland/Services/WebContent/ConnectionFromClient.cpp

@@ -18,6 +18,7 @@
 #include <LibJS/Parser.h>
 #include <LibJS/Runtime/ConsoleObject.h>
 #include <LibWeb/Bindings/MainThreadVM.h>
+#include <LibWeb/CSS/PropertyID.h>
 #include <LibWeb/Cookie/ParsedCookie.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/NodeList.h>
@@ -517,6 +518,49 @@ Messages::WebContentServer::GetElementPropertyResponse ConnectionFromClient::get
     return { string_or_error.release_value() };
 }
 
+Messages::WebContentServer::GetActiveDocumentsTypeResponse ConnectionFromClient::get_active_documents_type()
+{
+    auto* active_document = page().top_level_browsing_context().active_document();
+
+    if (!active_document)
+        return { "" };
+
+    auto type = active_document->document_type();
+
+    switch (type) {
+    case Web::DOM::Document::Type::HTML:
+        return { "html" };
+        break;
+    case Web::DOM::Document::Type::XML:
+        return { "xml" };
+        break;
+    }
+
+    return { "" };
+}
+
+Messages::WebContentServer::GetComputedValueForElementResponse ConnectionFromClient::get_computed_value_for_element(i32 element_id, String const& property_name)
+{
+    auto* node = Web::DOM::Node::from_id(element_id);
+    if (!node)
+        return { "" };
+
+    if (!node->is_element())
+        return { "" };
+
+    auto& element = verify_cast<Web::DOM::Element>(*node);
+
+    auto property_id = Web::CSS::property_id_from_string(property_name);
+
+    auto computed_values = element.computed_css_values();
+    if (!computed_values)
+        return { "" };
+
+    auto style_value = computed_values->property(property_id);
+
+    return { style_value->to_string() };
+}
+
 Messages::WebContentServer::GetSelectedTextResponse ConnectionFromClient::get_selected_text()
 {
     return page().focused_context().selected_text();

Userland/Services/WebContent/ConnectionFromClient.h

@@ -83,6 +83,8 @@ private:
     virtual Messages::WebContentServer::QuerySelectorAllResponse query_selector_all(i32 start_node_id, String const& selector) override;
     virtual Messages::WebContentServer::GetElementAttributeResponse get_element_attribute(i32 element_id, String const& name) override;
     virtual Messages::WebContentServer::GetElementPropertyResponse get_element_property(i32 element_id, String const& name) override;
+    virtual Messages::WebContentServer::GetActiveDocumentsTypeResponse get_active_documents_type() override;
+    virtual Messages::WebContentServer::GetComputedValueForElementResponse get_computed_value_for_element(i32 element_id, String const& property_name) override;
 
     virtual Messages::WebContentServer::GetLocalStorageEntriesResponse get_local_storage_entries() override;
     virtual Messages::WebContentServer::GetSessionStorageEntriesResponse get_session_storage_entries() override;

Userland/Services/WebContent/WebContentServer.ipc

@@ -41,6 +41,8 @@ endpoint WebContentServer
     query_selector_all(i32 start_node_id, String selector) => (Optional<Vector<i32>> elements_ids)
     get_element_attribute(i32 element_id, String name) => (Optional<String> attribute)
     get_element_property(i32 element_id, String name) => (Optional<String> property)
+    get_active_documents_type() => (String type)
+    get_computed_value_for_element(i32 element_id, String property_name) => (String computed_value)
 
     run_javascript(String js_source) =|