Make QWindow backed QOffscreenSurfaces easier to identify

Change-Id: I2b4d9b752f4b356cb3b0019dcfd4aab2edc30e94
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/gui/kernel/qoffscreensurface.cpp

@@ -177,6 +177,7 @@ void QOffscreenSurface::create()
             if (QThread::currentThread() != qGuiApp->thread())
                 qWarning("Attempting to create QWindow-based QOffscreenSurface outside the gui thread. Expect failures.");
             d->offscreenWindow = new QWindow(d->screen);
+            d->offscreenWindow->setObjectName("QOffscreenSurface");
             // Remove this window from the global list since we do not want it to be destroyed when closing the app.
             // The QOffscreenSurface has to be usable even after exiting the event loop.
             QGuiApplicationPrivate::window_list.removeOne(d->offscreenWindow);