LibGUI: Add a new Window::is_maximized method

Libraries/LibGUI/Window.cpp

@@ -682,6 +682,14 @@ void Window::set_fullscreen(bool fullscreen)
     WindowServerConnection::the().send_sync<Messages::WindowServer::SetFullscreen>(m_window_id, fullscreen);
 }
 
+bool Window::is_maximized() const
+{
+    if (!is_visible())
+        return false;
+
+    return WindowServerConnection::the().send_sync<Messages::WindowServer::IsMaximized>(m_window_id)->maximized();
+}
+
 void Window::schedule_relayout()
 {
     if (m_layout_pending)

Libraries/LibGUI/Window.h

@@ -64,6 +64,8 @@ public:
     bool is_fullscreen() const { return m_fullscreen; }
     void set_fullscreen(bool);
 
+    bool is_maximized() const;
+
     bool is_frameless() const { return m_frameless; }
     void set_frameless(bool frameless) { m_frameless = frameless; }