Oh, this is an internal class of our project and I had used it without realizing the source.
Anyway, the idea is to wrap the InternalRow in a class that derives from Row. When you implement the functions of the trait 'Row ', the type conversions from Row types to InternalRow types has to be done for each of the types. But, as I can see, the primitive types (apart from String) don't need conversions. Map and Array would need some handling.
I will check with the author of this code, I think this code can be contributed to Spark.