Policies coming from policy::BrowserPolicyConnector::SetPolicyProviderForTesting apply globally, i.e. to all profiles, including the sign-in profile.

This causes warnings in browsertests (e.g. force-installing extensions which are not allowed in the sign-in profile) and could cause more weird behavior.
Note that the sign-in profile ("Default") always exists, even when not running with --login-manager:
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/chrome_browser_main_chromeos.cc?rcl=b4a4e4e57e29d2c8404704878ad154452188fe90&l=917

In contrast, Cloud Policy does _not_ apply to the sign-in profile, this is implemented in UserPolicyManagerFactoryChromeOS:
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/policy/user_policy_manager_factory_chromeos.cc?rcl=409b9c00941963df196bd1356893d2e777ae4e44&l=175
( There are however a few device policies "mapped" to user policies of the sign-in profile using LoginProfilePolicyProvider:
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/policy/login_profile_policy_provider.cc?rcl=b4a4e4e57e29d2c8404704878ad154452188fe90&l=144 )

I think that most tests using BrowserPolicyConnector::SetPolicyProviderForTesting would be better off using ProfilePolicyConnectorFactory::PushProviderForTesting, which sets the testing policy provider for the next Profile which will be initialized.
If we agree that this would be better, we should re-evaluate existing tests and change them to use it if it matches better, and document on the two functions what scope they apply to.