Thanks for your data and project.
The default bounding box of your data is "389219.695288,2057987.554821,396320.5484,2050449.939274", I get it like this:
RectangleShape rect = shapeFileFeatureLayer.GetBoundingBox();
That means your data is not under decimal degree(is not 4326) and the unit should be meter, and because it don't cover the Google map, that means its projection is not 3857(900913) also.
I checked your data and hadn't found the .prj file, so we don't know what's the projection of your data, that's why it don't works.
Because shape file don't contains projection information, so the solution is get the projection information from your data provider and then you can reprojection it to make it works with Google.