QmlProfiler: Add functions to check if timeline view is usable

We can only use the timeline view if the scene graph is rendered via
OpenGL. This can be checked from Qt 5.8 on by querying the
RendererInterface. Earlier versions of Qt can only render with OpenGL.

Change-Id: I3f77e2a4dee1f9a1df5d6b1946cf7eb05a1bad01
Task-number: QTCREATORBUG-16503
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/qmlprofiler/qmlprofilerviewmanager.cpp

@@ -147,6 +147,11 @@ void QmlProfilerViewManager::restrictEventsToRange(qint64 rangeStart, qint64 ran
     d->profilerModelManager->restrictToRange(rangeStart, rangeEnd);
 }
 
+bool QmlProfilerViewManager::isTimelineUsable() const
+{
+    return d->traceView->isUsable();
+}
+
 void QmlProfilerViewManager::raiseTimeline()
 {
     QTC_ASSERT(qobject_cast<QDockWidget *>(d->traceView->parentWidget()), return);