The JSON file is generated as follows.
1. Go to the src/chrome/app/resources directory of Chromium's source.
2. Find the translation ID of the "Allow access to file URLs" string:
grep 'Allow access to file URLs' generated_resources_en-GB.xtb
3. With the ID that you've found, locate the other translations.
grep 3341703758641437857 generated_resources_*.xtb
4. If the result looks OK, serialize the result as JSON and save it.
> path/to/pdf.js/web/chrome-i18n-allow-access-to-file-urls.json \
python -c "import json;print(json.dumps({ \
$(grep 3341703758641437857 generated_resources_*.xtb | \
sed "s@generated_resources_\([^.]\+\)\.xtb:<translation[^>]\+>\(.\+\)</translation>@'\1':'''\2''',@" \
)}, sort_keys=True, indent=2))"
(Strings are taken from Chromium 45.0.2448.0 (ccrev.com/337313).
