In QtWebKit, we could use:
Looking at the source "here":https://qt.gitorious.org/qt/qtwebengine/source/ca30d0374020752d3ac367fdffef88a5c1fe4a48:src/webengine/api/qquickwebengineview.cpp#L599, it seems that it is still an experimental feature which means it will not be available currently in WebEngineView.
To try out those features you can try importing experimental module
import QtWebEngine.experimental 1.0
but note that these are still under development and the behavior may be erratic.
To follow this development you can ask the question on "Interest Mailing List":http://lists.qt-project.org/mailman/listinfo/interest, you might get an answer directly from the Qt developers. You will need to subscribe to the list first.