Don't drop update requests when closing and reopening windows

Before commit 4d15f393a7 update requests
were handled by a timer on QWindow. Therefore they survived the closing
and re-opening of platform windows. Now, as the timer was moved to
QPlatformWindow, it gets reset when you close the QWindow, and any
pending update requests are lost. However, we do set the
updateRequestPending variable on QWindow when requesting an update.
Therefore, we can also restore the update timer on the platform window
when creating it.

Change-Id: I23b00f24a46706beac7d1455edd8a5623db46b22
Fixes: QTBUG-70957
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/gui/kernel/qwindow.cpp

@@ -546,6 +546,9 @@ void QWindowPrivate::create(bool recursive, WId nativeHandle)
 
     QPlatformSurfaceEvent e(QPlatformSurfaceEvent::SurfaceCreated);
     QGuiApplication::sendEvent(q, &e);
+
+    if (updateRequestPending)
+        platformWindow->requestUpdate();
 }
 
 void QWindowPrivate::clearFocusObject()

tests/auto/gui/kernel/qwindow/tst_qwindow.cpp

@@ -29,6 +29,7 @@
 #include <qrasterwindow.h>
 #include <qpa/qwindowsysteminterface.h>
 #include <qpa/qplatformintegration.h>
+#include <qpa/qplatformwindow.h>
 #include <private/qguiapplication_p.h>
 #include <private/qhighdpiscaling_p.h>
 #include <QtGui/QPainter>
@@ -114,6 +115,7 @@ private slots:
     void cleanup();
     void testBlockingWindowShownAfterModalDialog();
     void generatedMouseMove();
+    void keepPendingUpdateRequests();
 
 private:
     QPoint m_availableTopLeft;
@@ -2451,6 +2453,27 @@ void tst_QWindow::generatedMouseMove()
     QVERIFY(w.mouseMovedCount == 5);
 }
 
+void tst_QWindow::keepPendingUpdateRequests()
+{
+    QRect geometry(m_availableTopLeft + QPoint(80, 80), m_testWindowSize);
+
+    Window window;
+    window.setGeometry(geometry);
+    window.show();
+    QCoreApplication::processEvents();
+    QTRY_VERIFY(window.isExposed());
+
+    window.requestUpdate();
+    window.close();
+    window.setVisible(true);
+
+    QPlatformWindow *platformWindow = window.handle();
+    QVERIFY(platformWindow);
+
+    QVERIFY(platformWindow->hasPendingUpdateRequest());
+    QTRY_VERIFY(!platformWindow->hasPendingUpdateRequest());
+}
+
 #include <tst_qwindow.moc>
 QTEST_MAIN(tst_QWindow)