[Passwords] Blacklist in the profile store for not-opted in butter users

The functionality is already implemented and even tested :-)
This CL is only add a comment to make the design decision more explicit!


Bug: 1012203
Change-Id: Ib62c51ab924e3172deffde7b8bc036f2ee824c48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2127106
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754987}

components/password_manager/core/browser/multi_store_password_save_manager.cc

@@ -157,6 +157,8 @@ void MultiStorePasswordSaveManager::PermanentlyBlacklist(
           PasswordForm::Store::kAccountStore) {
     account_store_form_saver_->PermanentlyBlacklist(form_digest);
   } else {
+    // For users who aren't yet opted-in to the account storage, we store their
+    // blacklisted entries in the profile store.
     form_saver_->PermanentlyBlacklist(form_digest);
   }
 }