Introduce QWindowSystemInterface::handleSynchronousCloseEvent

And use it from the Cocoa backend.

In general, for threaded GL rendering to work, any function that
affect the surface must be synchronous, so the implementor (such as
QQuickCanvas) can pick it up and block until the GL context has
released the surface. Otherwise, we will crash.

Change-Id: Id8484dac7452fe96fa80ade4ea321145f32124b4
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/gui/kernel/qwindowsysteminterface_qpa.cpp

@@ -108,6 +108,14 @@ void QWindowSystemInterface::handleCloseEvent(QWindow *tlw)
     }
 }
 
+void QWindowSystemInterface::handleSynchronousCloseEvent(QWindow *tlw)
+{
+    if (tlw) {
+        QWindowSystemInterfacePrivate::CloseEvent e(tlw);
+        QGuiApplicationPrivate::processWindowSystemEvent(&e);
+    }
+}
+
 /*!
 
 \a tlw == 0 means that \a ev is in global coords only

src/gui/kernel/qwindowsysteminterface_qpa.h

@@ -98,6 +98,7 @@ public:
     static void handleGeometryChange(QWindow *w, const QRect &newRect);
     static void handleSynchronousGeometryChange(QWindow *w, const QRect &newRect);
     static void handleCloseEvent(QWindow *w);
+    static void handleSynchronousCloseEvent(QWindow *w);
     static void handleEnterEvent(QWindow *w);
     static void handleLeaveEvent(QWindow *w);
     static void handleWindowActivated(QWindow *w);

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -233,7 +233,7 @@ void QCocoaWindow::windowDidResize()
 
 void QCocoaWindow::windowWillClose()
 {
-    QWindowSystemInterface::handleCloseEvent(window());
+    QWindowSystemInterface::handleSynchronousCloseEvent(window());
 }
 
 void QCocoaWindow::setCurrentContext(QCocoaGLContext *context)