Accessing contentsSize too soon crashes

import QtQuick 2.8
import QtQuick.Window 2.2
import QtWebEngine 1.3

Window {
    visible: true
    width: 640
    height: 480

    WebEngineView {
        Component.onCompleted: console.log("Boom!", contentsSize)
    }
}

#0  0x00007fffca009354 in QtWebEngineCore::WebContentsAdapter::lastContentsSize() const () from /usr/lib/x86_64-linux-gnu/libQt5WebEngineCore.so.5
#1  0x00007fffd5d3f771 in QQuickWebEngineView::contentsSize() const () from /usr/lib/x86_64-linux-gnu/libQt5WebEngine.so.5
#2  0x00007fffd5d554f0 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5WebEngine.so.5
#3  0x00007fffd5d55f0b in QQuickWebEngineView::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5WebEngine.so.5
#4  0x00007ffff7354d95 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#5  0x00007ffff7355ae8 in QV4::QQmlValueTypeWrapper::get(QV4::Managed const*, QV4::String*, bool*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#6  0x00007ffff72b1431 in QV4::RuntimeHelpers::objectDefaultValue(QV4::Object const*, int) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#7  0x00007ffff72b5d6a in QV4::Value::toQStringNoThrow() const () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#8  0x00007ffff7376e24 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#9  0x00007ffff72b358e in QV4::Runtime::method_callProperty(QV4::ExecutionEngine*, int, QV4::CallData*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#10 0x00007ffff72a9c28 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#11 0x00007ffff72ab373 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#12 0x00007ffff7227e3c in QV4::ExecutionContext::call(QV4::Scope&, QV4::CallData*, QV4::Function*, QV4::FunctionObject const*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#13 0x00007ffff73474f1 in QQmlJavaScriptExpression::evaluate(QV4::CallData*, bool*, QV4::Scope&) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#14 0x00007ffff72e01bb in QQmlBoundSignalExpression::evaluate(void**) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#15 0x00007ffff72e161b in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#16 0x00007ffff73239c7 in QQmlNotifier::emitNotify(QQmlNotifierEndpoint*, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#17 0x00007ffff72c31e4 in QQmlData::signalEmitted(QAbstractDeclarativeData*, QObject*, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#18 0x00007ffff6bfc97e in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#19 0x00007ffff735a960 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#20 0x00007ffff72d68ce in QQmlComponentPrivate::complete(QQmlEnginePrivate*, QQmlComponentPrivate::ConstructionState*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#21 0x00007ffff72d69e7 in QQmlComponentPrivate::completeCreate() () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
#22 0x00007ffff72d67ba in QQmlComponent::create(QQmlContext*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5