Using the ee.Reducer.sum() to count the area of different classes of a layer (hansen/global_forest_change_2017_v1_5)

I have used the following function to calculate the area of an area of interest (AOI) of a classification using landsat8 images.
This counts the area in square meters of the classification for a given polygon.

var areaChart = ui.Chart.image.byClass({
  image: ee.Image.pixelArea().addBands(lista_imagenes[0]),
  classBand: 'classification', 
  region: geometry,
  scale: 30,
  reducer: ee.Reducer.sum()
});

The problem is that the band of classification of landsat8 is just one (classification band). And the layer I am using has three layers (it is call year of loss).

There is any way to count the classes of the layer given a polygon using a similar question?

Here the code:
https://code.earthengine.google.com/495ed315756b7181b4570546be82e2f4