Add reuasable Gitlab::Tracking::Helpers module

There are several controllers/concerns/modules that checks for the
DNT header and the logic are the same.

To make them DRY, a new Gitlab::Tracking::Helpers module was added
to encapsulate the following methods:
- `dnt_enabled?`
- `trackable_html_request?`

app/controllers/admin/cohorts_controller.rb

@@ -21,8 +21,6 @@ class Admin::CohortsController < Admin::ApplicationController
   end
 
   def track_cohorts_visit
-    if request.format.html? && request.headers['DNT'] != '1'
-      track_visit('i_analytics_cohorts')
-    end
+    track_visit('i_analytics_cohorts') if trackable_html_request?
   end
 end

app/controllers/concerns/redis_tracking.rb

@@ -12,12 +12,13 @@
 # You can also pass custom conditions using `if:`, using the same format as with Rails callbacks.
 # You can also pass an optional block that calculates and returns a custom id to track.
 module RedisTracking
+  include Gitlab::Tracking::Helpers
   extend ActiveSupport::Concern
 
   class_methods do
     def track_redis_hll_event(*controller_actions, name:, if: nil, &block)
       custom_conditions = Array.wrap(binding.local_variable_get('if'))
-      conditions = [:trackable_request?, *custom_conditions]
+      conditions = [:trackable_html_request?, *custom_conditions]
 
       after_action only: controller_actions, if: conditions do
         track_unique_redis_hll_event(name, &block)
@@ -37,10 +38,6 @@ module RedisTracking
     Gitlab::UsageDataCounters::HLLRedisCounter.track_event(event_name, values: unique_id)
   end
 
-  def trackable_request?
-    request.format.html? && request.headers['DNT'] != '1'
-  end
-
   def visitor_id
     return cookies[:visitor_id] if cookies[:visitor_id].present?
     return unless current_user

app/controllers/projects/merge_requests/diffs_controller.rb

@@ -193,7 +193,7 @@ class Projects::MergeRequests::DiffsController < Projects::MergeRequests::Applic
   end
 
   def track_viewed_diffs_events
-    return if request.headers['DNT'] == '1'
+    return if dnt_enabled?
 
     Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter
       .track_mr_diffs_action(merge_request: @merge_request)

app/helpers/analytics/unique_visits_helper.rb

@@ -2,6 +2,7 @@
 
 module Analytics
   module UniqueVisitsHelper
+    include Gitlab::Tracking::Helpers
     extend ActiveSupport::Concern
 
     def visitor_id
@@ -21,7 +22,7 @@ module Analytics
 
     class_methods do
       def track_unique_visits(controller_actions, target_id:)
-        after_action only: controller_actions, if: -> { request.format.html? && request.headers['DNT'] != '1' } do
+        after_action only: controller_actions, if: -> { trackable_html_request? } do
           track_visit(target_id)
         end
       end

lib/gitlab/experimentation/controller_concern.rb

@@ -11,6 +11,7 @@ module Gitlab
   module Experimentation
     module ControllerConcern
       include ::Gitlab::Experimentation::GroupTypes
+      include Gitlab::Tracking::Helpers
       extend ActiveSupport::Concern
 
       included do
@@ -101,10 +102,6 @@ module Gitlab
 
       private
 
-      def dnt_enabled?
-        Gitlab::Utils.to_boolean(request.headers['DNT'])
-      end
-
       def experimentation_subject_id
         cookies.signed[:experimentation_subject_id]
       end

lib/gitlab/tracking/helpers.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Tracking
+    module Helpers
+      def dnt_enabled?
+        Gitlab::Utils.to_boolean(request.headers['DNT'])
+      end
+
+      def trackable_html_request?
+        request.format.html? && !dnt_enabled?
+      end
+    end
+  end
+end