Increase test coverage for more of the existing branches. (at least one test for every modified field was added in flutter/engine#44724)
Then convert addPointerForIndex and related methods to set values on a class (InputData?) then write a function to write the bytebuffer "packet" from a complete input data. This would make the code easier to test and make it harder for accidental changes to the byte format.

io/flutter/embedding/android/AndroidTouchProcessor.java