QmlJsDebugger: Fix observer navigation on Mac OS X

Seems that mouse events aren't sent through the viewport on Mac OS X.

share/qtcreator/qml/qmljsdebugger/qdeclarativeviewobserver.cpp

@@ -80,6 +80,7 @@ QDeclarativeViewObserver::QDeclarativeViewObserver(QDeclarativeView *view, QObje
     data->currentTool = data->selectionTool;
 
     data->view->setMouseTracking(true);
+    data->view->installEventFilter(this);
     data->view->viewport()->installEventFilter(this);
 
     data->debugService = QDeclarativeObserverService::instance();