Reported size change doesn't account for new files

[necolas]

I noticed that if a diff deletes a file and adds a new one, the deletion contributes to the "Size change" value but the addition does not. The new file is listed under "View unchanged". The "Total size" is accurate but unless someone pays attention to what the total size was in the last PR, they may be misled by a PR that claims to make a lot of savings but actually moves code around into new files and doesn't reduce the total size by much at all

[necolas]

I think this might actually be caused by build assets not being cleaned up between builds.