Any qml app using a QtWebkit WebView and a MainView fail to load on the device

On the UbuntuPhone device (Vivid or RTM based), any app as simple as:

MainView {
    Page { WebView { } }
}

fails to load, the app load spinner does on forever.

To reproduce it:

- open QtC,
- create a blank simple qml project,
- mofidy the project main qml file to add a WebView in the Mainview's page, e.g

import QtQuick 2.0
import Ubuntu.Components 1.1
import QtWebKit 3.0

MainView {
    applicationName: "webkit.abreu-alexandre"

    // Removes the old toolbar and enables new features of the new header.
    useDeprecatedToolbar: false

    width: units.gu(100)
    height: units.gu(75)

    Page {
        title: i18n.tr("Simple")

        Column {
            spacing: units.gu(1)
            anchors {
                margins: units.gu(2)
                fill: parent
            }
            WebView {

            }
        }
    }
}

- launch the app on the device