[autofill] Fix autofill::prefs::kAutofillProfileValidity

The value of the autofill::prefs::kAutofillProfileValidity pref
name does not match the actual value being used to populate the
priority pref from the server.

Thie CL changes this constant from autofill.profile_validity to
autofill_profile_validity to match what's actually being synced.

Change-Id: I151874de8dde861dff280e1fc0e53e2ee1b60d84
Bug: 910596
Reviewed-on: https://chromium-review.googlesource.com/c/1356863
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612793}

components/autofill/core/common/autofill_prefs.cc

@@ -96,7 +96,10 @@ const char kAutofillOrphanRowsRemoved[] = "autofill.orphan_rows_removed";
 const char kAutofillProfileEnabled[] = "autofill.profile_enabled";
 
 // The field type, validity state map of all profiles.
-const char kAutofillProfileValidity[] = "autofill.profile_validity";
+// TODO(crbug.com/910596): Pref name is "autofill_" instead of "autofill."
+// because of a mismatch when the priorify prefs were generated. Consider
+// migrating this back to "autofill." in the future.
+const char kAutofillProfileValidity[] = "autofill_profile_validity";
 
 // The opt-ins for Sync Transport features for each client.
 const char kAutofillSyncTransportOptIn[] = "autofill.sync_transport_opt_ins";