commit 533da505f959bd687524f0974cb783976365a827
Author: Dmitry Kazakov <dimula73@gmail.com>
Date:   Thu Mar 31 14:30:04 2016 +0300

    Fix Enter/Leave events coming in a weird way due to a bug in XCB(?)

    Calling QApplication::topLevelAt/widgetAt() causes XCB go crazy and
    stop delivering Enter/Leave events. I don't know why it happens,
    but it affects on our implementation of tablet events. Vanilla Qt
    should not be affected. Though it also tries to use it as a fall-back
    case in QGuiApplicationPrivate::processTabletEvent...

    CC:Shawn.Rutledge@theqtcompany.com
    Ref T1591