Fixed mouse double click events not bubbling up to parent widgets.

The bug was caused by changes b371f3f943
and 3bb9024952, which removed the event
forwarding that QWidget::mouseDoubleClickEvent() used to do without
making sure to call ignore() on the event like
QWidget::mousePressEvent() does.

Task-number: QTBUG-29680
Change-Id: I98af8052ad3dd1dea15d07a710aa9212ef5e4a68
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/widgets/kernel/qwidget.cpp

@@ -8413,7 +8413,7 @@ void QWidget::mouseReleaseEvent(QMouseEvent *event)
 
 void QWidget::mouseDoubleClickEvent(QMouseEvent *event)
 {
-    Q_UNUSED(event);
+    event->ignore();
 }
 
 #ifndef QT_NO_WHEELEVENT

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -411,6 +411,7 @@ private slots:
     void destroyedSignal();
 
     void keyboardModifiers();
+    void mouseDoubleClickBubbling_QTBUG29680();
 
 private:
     bool ensureScreenSize(int width, int height);
@@ -10047,5 +10048,30 @@ void tst_QWidget::keyboardModifiers()
     QCOMPARE(int(w->m_appModifiers), int(Qt::ControlModifier));
 }
 
+class DClickWidget : public QWidget
+{
+public:
+    DClickWidget() : triggered(false) {}
+    void mouseDoubleClickEvent(QMouseEvent *)
+    {
+        triggered = true;
+    }
+    bool triggered;
+};
+
+void tst_QWidget::mouseDoubleClickBubbling_QTBUG29680()
+{
+    DClickWidget parent;
+    QWidget child(&parent);
+    parent.resize(200, 200);
+    child.resize(200, 200);
+    parent.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&parent));
+
+    QTest::mouseDClick(&child, Qt::LeftButton);
+
+    QTRY_VERIFY(parent.triggered);
+}
+
 QTEST_MAIN(tst_QWidget)
 #include "tst_qwidget.moc"