The programming model for Power BI custom visuals changes over the summer in 2016. In the older model, there is an init method for each custom visuals. When the model changed, developers now write init code for one-time load operations in class constructor and there is no longer an init method for custom visuals in the new model.
The example you are looking at is based on the old model and you should be able to move that code from the old init method into the constructor.