Record terms opt in experiment users

To have a better data quality, we want to also know which users
are part of the experiment. This should help us to filter out bots
from automatic sign up scripts.

We now also only track the end of the experiment phase only for
valid sign up data.

app/controllers/registrations_controller.rb

@@ -26,12 +26,12 @@ class RegistrationsController < Devise::RegistrationsController
   end
 
   def create
-    track_experiment_event(:terms_opt_in, 'end')
     accept_pending_invitations
 
     super do |new_user|
       persist_accepted_terms_if_required(new_user)
       set_role_required(new_user)
+      track_terms_experiment(new_user)
       yield new_user if block_given?
     end
 
@@ -201,6 +201,13 @@ class RegistrationsController < Devise::RegistrationsController
     true
   end
 
+  def track_terms_experiment(new_user)
+    return unless new_user.persisted?
+
+    track_experiment_event(:terms_opt_in, 'end')
+    record_experiment_user(:terms_opt_in)
+  end
+
   def load_recaptcha
     Gitlab::Recaptcha.load_configurations!
   end

spec/controllers/registrations_controller_spec.rb

@@ -316,6 +316,12 @@ RSpec.describe RegistrationsController do
           stub_experiment(signup_flow: true, terms_opt_in: true)
         end
 
+        it 'records user for the terms_opt_in experiment' do
+          expect(controller).to receive(:record_experiment_user).with(:terms_opt_in)
+
+          subject
+        end
+
         context 'when user is not part of the experiment' do
           before do
             stub_experiment_for_user(signup_flow: true, terms_opt_in: false)