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The goal is to whitelist logged EV certificates so the requirement of
CT for EV certificates can be enabled without waiting for all EV certs
to be re-issued.

This change adds the code for unpacking the list of (truncated) hashes
of EV certificates. The compressed data format is the diff values
between the hashes, encoded using Golomb coding. This was suggested
by agl as an efficient encoding, since the hash values of the
EV certificates are uniformly distributed, so the differences between
them are geometrically distributed. See section 4 in:
http://algo2.iti.kit.edu/singler/publications/cacheefficientbloomfilters-wea2007.pdf

The code that generates the data can be found here:
https://github.com/google/certificate-transparency/blob/master/python/utilities/ev_whitelist/golomb_code.py#L27

Currently the code is not hooked into anything, but once the
compressed list would be fetched as a component update, we'll start
by logging statistics about known vs. unknown EV certs.

BUG=339128

Review URL: https://codereview.chromium.org/462543002

Cr-Commit-Position: refs/heads/master@{#293288}