The sorted file list is split into contiguous chunks of roughly equal total
file size, using size as a stand-in for run time, so new test files are
included automatically and slow test files are spread across shards rather
than landing in the same shard by chance. Contiguous chunks preserve the
alphabetical run order of a full run, so files keep the same preceding files
as in a full run except at chunk starts, and a shard can be reproduced locally
by passing its first and last files to -s and -e.
XPCOM objects have to be statically registered now, so instead of
creating our own command-line handler, just stuff our code into the
Firefox one.
A few parameters require the Zotero object, which isn't available in the
Firefox CLH, so I've left those in zotero-service.js for now until we
decide how to deal with those.
