When updating src/net/base/registry_controlled_domains/effective_tld_names.dat:

1. Obtain the new effective_tld_names.dat, probably by downloading https://publicsuffix.org/list/public_suffix_list.dat
2. Remove whitespace from the ends of the lines. You could possibly use something like:

     sed -i -e "s/\s*$//g" \
         src/net/base/registry_controlled_domains/effective_tld_names.dat
   

3. Add the Chromium note back in just after the license at the top, and just before ‘===BEGIN ICANN DOMAINS===’. Ensure there is an empty line above and two empty lines below the note. The note should say:

   // Chromium note: this is based on Mozilla's file:
   // https://publicsuffix.org/list/public_suffix_list.dat
   

4. Diff the changes and restore any changes annotated with a // CHROMIUM comment.
5. Build the tld_cleanup target.
6. Run tld_cleanup (no arguments needed), typically from src/out/Default. It will re-generate src/net/base/registry_controlled_domains/effective_tld_names.gperf.
7. Check in the updated effective_tld_names.dat, effective_tld_names.gperf.

Note that gperf is no longer used for effective_tld_names, but when building Chromium, the file effective_tld_names.gperf will be parsed by make_dafsa.py to generate the file effective_tld_names-inc.cc, which is included in registry_controlled_domain.cc.