Make QApplicationPrivate::active_window private

The active window of QApplication overlaps largely with the focus window
of QGuiApplication. As a first step towards potentially removing the
active_window member, make it private so we control access to it.

Task-number: QTBUG-119287
Change-Id: I95785fea3ba4444db64063f4e4d3d3004465ef64
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/kernel/qapplication.cpp

@@ -310,7 +310,6 @@ QWidget *QApplication::topLevelAt(const QPoint &pos)
 */
 
 void qt_init_tooltip_palette();
-void qt_cleanup();
 
 QStyle *QApplicationPrivate::app_style = nullptr;        // default application style
 #ifndef QT_NO_STYLE_STYLESHEET
@@ -708,7 +707,10 @@ QApplication::~QApplication()
 
     d->cleanupMultitouch();
 
-    qt_cleanup();
+    QPixmapCache::clear();
+    QColormap::cleanup();
+
+    QApplicationPrivate::active_window = nullptr; //### this should not be necessary
 
     if (QApplicationPrivate::widgetCount)
         qDebug("Widgets left: %i    Max widgets: %i \n", QWidgetPrivate::instanceCounter, QWidgetPrivate::maxInstances);
@@ -719,14 +721,6 @@ QApplication::~QApplication()
     QApplicationPrivate::widgetCount = false;
 }
 
-void qt_cleanup()
-{
-    QPixmapCache::clear();
-    QColormap::cleanup();
-
-    QApplicationPrivate::active_window = nullptr; //### this should not be necessary
-}
-
 /*!
     \fn QWidget *QApplication::widgetAt(const QPoint &point)
 

src/widgets/kernel/qapplication_p.h

@@ -145,7 +145,6 @@ public:
     static QWidget *main_widget;
     static QWidget *focus_widget;
     static QWidget *hidden_focus_widget;
-    static QWidget *active_window;
 #if QT_CONFIG(wheelevent)
     static int  wheel_scroll_lines;
     static QPointer<QWidget> wheel_widget;
@@ -228,6 +227,7 @@ private:
     static void giveFocusAccordingToFocusPolicy(QWidget *w, QEvent *event, QPoint localPos);
     static bool shouldSetFocus(QWidget *w, Qt::FocusPolicy policy);
 
+    static QWidget *active_window;
 
     static bool isAlien(QWidget *);
 };

src/widgets/kernel/qwidget.cpp

@@ -12448,7 +12448,7 @@ void QWidget::destroy(bool destroyWindow, bool destroySubWindows)
     if ((windowType() == Qt::Popup) && qApp)
         qApp->d_func()->closePopup(this);
 
-    if (this == QApplicationPrivate::active_window)
+    if (this == qApp->activeWindow())
         QApplicationPrivate::setActiveWindow(nullptr);
     if (QWidget::mouseGrabber() == this)
         releaseMouse();