OSR: element with a running CSS animation keeps its last painted state after navigating away #548

import org.cef.CefApp;
import org.cef.CefClient;
import org.cef.CefSettings;
import org.cef.browser.CefBrowser;

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

/**
 * Swing/JCEF counterpart of the JavaFX reproducer: loads page A (which has a running CSS
 * animation), navigates to a plain solid-colour page B, and leaves the window up.
 *
 * Off-screen rendering, to match the CEFFX case.
 */
public class SwingStaleBandRepro {

    private static final String A = System.getProperty("a");
    private static final String B = System.getProperty("b");

    public static void main(String[] args) {
        if (!CefApp.startup(args)) {
            System.out.println("### startup failed");
            return;
        }
        CefSettings settings = new CefSettings();
        settings.windowless_rendering_enabled = true;   // OSR, as in the CEFFX report

        CefApp app = CefApp.getInstance(settings);
        CefClient client = app.createClient();
        CefBrowser browser = client.createBrowser(A, true /* OSR */, false);
        Component ui = browser.getUIComponent();

        SwingUtilities.invokeLater(() -> {
            JFrame frame = new JFrame("SWING-REPRO");
            JPanel content = new JPanel(new BorderLayout());
            content.setPreferredSize(new Dimension(900, 700));
            content.add(ui, BorderLayout.CENTER);
            frame.setContentPane(content);
            frame.pack();
            frame.setLocation(60, 60);
            frame.setVisible(true);

            // Same timeline as the JavaFX reproducer: let A render and animate, then navigate.
            new Timer(10_000, e -> {
                ((Timer) e.getSource()).stop();
                System.out.println("### navigating to " + B);
                browser.loadURL(B);
                new Timer(15_000, e2 -> {
                    ((Timer) e2.getSource()).stop();
                    System.out.println("### READY");
                    System.out.flush();
                }) {{ setRepeats(false); }}.start();
            }) {{ setRepeats(false); }}.start();
        });
    }
}