policy_prefs_browsertest currently does not support testing policies mapped to CrosSettings[1].

Still, we have a few entries in policy_templates.json which specify such a test[2]. We also have tests using unrelated prefs to test policy behavior as a hack [3].

All in all, we should add support for CrosSettings-mapped policies in these tests.

[1] https://cs.chromium.org/chromium/src/chrome/browser/policy/policy_prefs_browsertest.cc?rcl=0c0767bf3a9ae556406005b57b41d16d5ae2cd26&l=501
[2] https://cs.chromium.org/search/?q=file:policy_test_cases.json+%5C%22cros%5C.&sq=package:chromium&type=cs
[3] https://cs.chromium.org/chromium/src/chrome/test/data/policy/policy_test_cases.json?l=3100&rcl=b0e53acd2ae9fe474ee32a1fc631dad2dc182709