Browser: Implement listener for most config options

The only option leaved as TODO is ColorScheme.

Userland/Applications/Browser/BrowserWindow.cpp

@@ -526,4 +526,30 @@ void BrowserWindow::create_new_tab(URL url, bool activate)
         m_tab_widget->set_active_widget(&new_tab);
 }
 
+void BrowserWindow::config_string_did_change(String const& domain, String const& group, String const& key, String const& value)
+{
+    if (domain != "Browser" || group != "Preferences")
+        return;
+
+    if (key == "SearchEngine")
+        Browser::g_search_engine = value;
+    else if (key == "Home")
+        Browser::g_home_url = value;
+
+    // TODO: ColorScheme    
+}
+
+void BrowserWindow::config_bool_did_change(String const& domain, String const& group, String const& key, bool value)
+{
+    if (domain != "Browser" || group != "Preferences")
+        return;
+
+    if (key == "ShowBookmarksBar") {
+        m_window_actions.show_bookmarks_bar_action().set_checked(value);
+        Browser::BookmarksBarWidget::the().set_visible(value);
+    }
+
+    // NOTE: CloseDownloadWidgetOnFinish is read each time in DownloadWindow
+}
+
 }

Userland/Applications/Browser/BrowserWindow.h

@@ -10,6 +10,7 @@
 #include "BookmarksBarWidget.h"
 #include "Tab.h"
 #include "WindowActions.h"
+#include <LibConfig/Listener.h>
 #include <LibGUI/ActionGroup.h>
 #include <LibGUI/Window.h>
 
@@ -18,7 +19,8 @@ namespace Browser {
 class CookieJar;
 class Tab;
 
-class BrowserWindow final : public GUI::Window {
+class BrowserWindow final : public GUI::Window
+    , public Config::Listener {
     C_OBJECT(BrowserWindow);
 
 public:
@@ -45,6 +47,9 @@ private:
     ErrorOr<void> load_search_engines(GUI::Menu& settings_menu);
     void set_window_title_for_tab(Tab const&);
 
+    virtual void config_string_did_change(String const& domain, String const& group, String const& key, String const& value) override;
+    virtual void config_bool_did_change(String const& domain, String const& group, String const& key, bool value) override;
+
     RefPtr<GUI::Action> m_go_back_action;
     RefPtr<GUI::Action> m_go_forward_action;
     RefPtr<GUI::Action> m_go_home_action;

Userland/Applications/Browser/main.cpp

@@ -67,6 +67,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     auto app = GUI::Application::construct(arguments);
 
     Config::pledge_domain("Browser");
+    Config::monitor_domain("Browser");
 
     // Connect to LaunchServer immediately and let it know that we won't ask for anything other than opening
     // the user's downloads directory.