set new tab menu icon

src/app/browser.cpp

@@ -45,6 +45,10 @@ Browser::Header::Tab::Tab()
     set_tooltip_text(
         TOOLTIP
     );
+
+    set_icon_name(
+        ICON
+    );
 }
 
 Browser::Container::Container()

src/app/browser.h

@@ -39,6 +39,7 @@ namespace app
                     {
                         public:
 
+                            const Glib::ustring ICON = "tab-new-symbolic";
                             const Glib::ustring TOOLTIP = "New tab";
 
                             Tab();