LibWebView+WebContent: Inform WebContent process if browser is headless

Author: https://github.com/tcl3
Commit: e764df15eb
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/2858
Reviewed-by: https://github.com/trflynn89

Services/WebContent/PageClient.h

@@ -34,6 +34,9 @@ public:
     };
     static void set_use_skia_painter(UseSkiaPainter);
 
+    virtual bool is_headless() const override;
+    static void set_is_headless(bool);
+
     virtual bool is_ready_to_paint() const override;
 
     virtual Web::Page& page() override { return *m_page; }