Enable system NSS key slot.

This only affects users of domains that the device is registered to for policy.
All other users are unaffected (EnableNSSSystemKeySlotForResourceContext is only called for USER_AFFILIATION_MANAGED)

For the affected users, this enables and uses the slot for
- client authentication for TSL (see ClientCertStoreChromeOS)
- client authentication for 802.1x networks
- listing/removing certificates on the settings page (see CertificateManager)

In a follow up, also the enterprise.platformKeys API will be updated.

Depends on:
https://codereview.chromium.org/426983002/
https://codereview.chromium.org/428933002/

BUG=210525
R=mattm@chromium.org, rsleevi@chromium.org, willchan@chromium.org, xiyuan@chromium.org

Review URL: https://codereview.chromium.org/424523002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@287175 0039d316-1c4b-4281-b951-d872f2087c98

• chrome/browser/chromeos/net/cert_verify_proc_chromeos.cc[diff]
• chrome/browser/net/nss_context.h[diff]
• chrome/browser/net/nss_context_chromeos.cc[diff]
• chrome/browser/profiles/profile_io_data.cc[diff]
• chrome/browser/profiles/profile_io_data.h[diff]
• crypto/nss_util.cc[diff]
• crypto/nss_util_internal.h[diff]
• crypto/scoped_test_nss_db.h[diff]
• crypto/scoped_test_system_nss_key_slot.cc[diff]
• crypto/scoped_test_system_nss_key_slot.h[diff]
• net/cert/nss_cert_database.cc[diff]
• net/cert/nss_cert_database.h[diff]
• net/cert/nss_cert_database_chromeos.cc[diff]
• net/cert/nss_cert_database_chromeos.h[diff]
• net/cert/nss_profile_filter_chromeos.cc[diff]
• net/cert/nss_profile_filter_chromeos.h[diff]
• net/cert/nss_profile_filter_chromeos_unittest.cc[diff]
• net/ssl/client_cert_store_chromeos.cc[diff]
• net/ssl/client_cert_store_chromeos.h[diff]
• net/ssl/client_cert_store_chromeos_unittest.cc[diff]