Process initial expose events immediately.

Required to prevent qmlscene flicker on startup.

Also brings back that qWait() in tst_QGL::graphicsViewClipping()
that seems necessary after all.

Amended-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Change-Id: I14ba6e18ac98e5df1ce8ecbc263b30176b67d111
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -320,6 +320,7 @@ void QCocoaWindow::setVisible(bool visible)
         // - QNSViews for child windows are initialy not hidden and won't get the
         //   viewDidUnhide message.
         exposeWindow();
+        QWindowSystemInterface::flushWindowSystemEvents();
 
         if (m_nsWindow) {
             // setWindowState might have been called while the window was hidden and

tests/auto/opengl/qgl/tst_qgl.cpp

@@ -875,6 +875,10 @@ void tst_QGL::graphicsViewClipping()
     scene.setSceneRect(view.viewport()->rect());
 
     QVERIFY(QTest::qWaitForWindowExposed(&view));
+    #ifdef Q_OS_MAC
+        // The black rectangle jumps from the center to the upper left for some reason.
+        QTest::qWait(100);
+    #endif
 
     QTRY_VERIFY(widget->painted);