The format pre-pass and the importer read the same inflated archive, where each
unzipped the file for itself, and a picture is encoded through the browser's
Uint8Array.toBase64, the chunked loop standing in where there is none.
On a 14 MB file holding 600 pictures that takes 250 ms of inflating and 285 ms of
encoding off the open: it lands 480 ms earlier and settles 240 ms earlier, and a
small illustrated file lands 170 ms earlier.
Steffen Becker
6693d04313