function preProcessEvent( tracker, eventInfo ) {
        eventInfo.eventSource = tracker;
        eventInfo.eventPhase = eventInfo.originalEvent ?
                        ((typeof eventInfo.originalEvent.eventPhase !== 'undefined') ?
                                            eventInfo.originalEvent.eventPhase : 0) : 0;
        eventInfo.defaultPrevented = $.eventIsCanceled( eventInfo.originalEvent );
        eventInfo.shouldCapture = false;
        eventInfo.shouldReleaseCapture = false;
        eventInfo.userData = tracker.userData;

        getEventProcessDefaults( tracker, eventInfo );

        if ( tracker.preProcessEventHandler ) {
            tracker.preProcessEventHandler( eventInfo );
        }
    }
Sets up for and calls preProcessEventHandler. Call with the following parameters -
this function will fill in the rest of the preProcessEventHandler event object
properties

@function
@private
@inner
@param {OpenSeadragon.MouseTracker} tracker
    A reference to the MouseTracker instance.
@param {OpenSeadragon.MouseTracker.EventProcessInfo} eventInfo
@param {Object} eventInfo.originalEvent
@param {String} eventInfo.eventType
@param {String} eventInfo.pointerType
@param {Boolean} eventInfo.isEmulated