Stabilize tst_QQuickView::resizemodeitem

FAIL!  : tst_QQuickView::resizemodeitem() Compared values are not the same
    Actual   (sizeListener.at(i)): QSize(80x100)
    Expected (view->size())      : QSize(200x300)
    Loc: [tst_qquickview.cpp(172)]

The "SizeChangesListener" can be instantiated too early, catching
signals from the previous resize events. Make sure to flush all events
before.

Change-Id: Ib0933429f5c589f120c263619f00893fa813e361
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

tests/auto/quick/qquickview/tst_qquickview.cpp

@@ -162,6 +162,7 @@ void tst_QQuickView::resizemodeitem()
     QCOMPARE(QSize(item->width(), item->height()), view->sizeHint());
 
     // size update from view
+    QCoreApplication::processEvents(); // make sure the last resize events are gone
     SizeChangesListener sizeListener(item);
     view->resize(QSize(200,300));
     QTRY_COMPARE(item->width(), 200.0);