[BEAM-11249] Read larger chunks for dataframe sources.
[BEAM-11249] Read larger chunks for dataframe sources.

A typical csv might have 10-1k bytes per line; the chunksize of 100
would result in kb-sized chunks.  Bumping this up brings us into the
mb-sized range.

lukecwik/incubator-beam,chamikaramj/beam,lukecwik/incubator-beam,chamikaramj/beam,apache/beam,lukecwik/incubator-beam,robertwb/incubator-beam,chamikaramj/beam,lukecwik/incubator-beam,apache/beam,chamikaramj/beam,apache/beam,robertwb/incubator-beam,apache/beam,chamikaramj/beam,robertwb/incubator-beam,lukecwik/incubator-beam,robertwb/incubator-beam,chamikaramj/beam,robertwb/incubator-beam,lukecwik/incubator-beam,chamikaramj/beam,apache/beam,robertwb/incubator-beam,chamikaramj/beam,apache/beam,lukecwik/incubator-beam,chamikaramj/beam,apache/beam,robertwb/incubator-beam,robertwb/incubator-beam,robertwb/incubator-beam,apache/beam,robertwb/incubator-beam,lukecwik/incubator-beam,apache/beam,lukecwik/incubator-beam,apache/beam,lukecwik/incubator-beam,apache/beam,chamikaramj/beam