Add A/B testing support to onboarding

As well as checking if we're gitlab.com and the
:user_onboarding feature flag is enabled, let's
roll the dice with an A/B test controlled by the
:experiment_growth_onboarding feature flag.

app/controllers/dashboard/projects_controller.rb

@@ -3,6 +3,7 @@
 class Dashboard::ProjectsController < Dashboard::ApplicationController
   include ParamsBackwardCompatibility
   include RendersMemberAccess
+  include OnboardingExperimentHelper
 
   prepend_before_action(only: [:index]) { authenticate_sessionless_user!(:rss) }
   before_action :set_non_archived_param

ee/app/controllers/ee/dashboard/projects_controller.rb

@@ -5,23 +5,26 @@ module EE
     module ProjectsController
       extend ActiveSupport::Concern
       extend ::Gitlab::Utils::Override
+      include ::OnboardingExperimentHelper
 
       private
 
       override :render_projects
       def render_projects
-        if show_onboarding_welcome_page?
-          redirect_to explore_onboarding_index_path
-        else
-          super
-        end
+        return redirect_to explore_onboarding_index_path if show_onboarding_welcome_page?
+
+        super
       end
 
       def show_onboarding_welcome_page?
-        return false unless ::Gitlab.com?
-        return false if cookies['onboarding_dismissed'] == 'true'
+        return false if onboarding_cookie_set?
+        return false unless allow_access_to_onboarding?
+
+        !show_projects?(projects, params)
+      end
 
-        ::Feature.enabled?(:user_onboarding) && !show_projects?(projects, params)
+      def onboarding_cookie_set?
+        cookies['onboarding_dismissed'] == 'true'
       end
     end
   end

ee/app/controllers/explore/onboarding_controller.rb

 # frozen_string_literal: true
 
 class Explore::OnboardingController < Explore::ApplicationController
+  include ::OnboardingExperimentHelper
+
   before_action :authenticate_user!
   before_action :set_project!
 
@@ -17,8 +19,6 @@ class Explore::OnboardingController < Explore::ApplicationController
   end
 
   def get_onboarding_demo_project
-    if Gitlab.com? && Feature.enabled?(:user_onboarding)
-      Project.find_by_full_path("gitlab-org/gitlab-ce")
-    end
+    Project.find_by_full_path("gitlab-org/gitlab-ce") if allow_access_to_onboarding?
   end
 end

ee/app/helpers/ee/application_helper.rb

@@ -3,6 +3,8 @@
 module EE
   module ApplicationHelper
     extend ::Gitlab::Utils::Override
+    include ::OnboardingExperimentHelper
+
     DB_LAG_SHOW_THRESHOLD = 60 # seconds
     LOG_CURSOR_CHECK_TIME = ::Gitlab::Geo::LogCursor::Daemon::SECONDARY_CHECK_INTERVAL
     EVENT_PROCESSING_TIME = 60.seconds
@@ -118,7 +120,7 @@ module EE
     end
 
     def user_onboarding_enabled?
-      ::Gitlab.com? && ::Feature.enabled?(:user_onboarding)
+      allow_access_to_onboarding?
     end
 
     private