Merge branch 'if-doc-ee_specific_api-params' into 'master'

Update development doc on EE specific API params

See merge request gitlab-org/gitlab-ce!28608

doc/development/ee_features.md

@@ -557,40 +557,56 @@ due to `prepend`, but Grape is complex internally and we couldn't easily do
 that, so we'll follow regular object-oriented practices that we define the
 interface first here.
 
-For example, suppose we have a few more optional params for EE, given this CE
-API code:
+For example, suppose we have a few more optional params for EE. We can move the
+params out of the `Grape::API` class to a helper module, so we can `prepend` it
+before it would be used in the class.
 
 ```ruby
 module API
-  class MergeRequests < Grape::API
-    # EE::API::MergeRequests would override the following helpers
-    helpers do
-      params :optional_params_ee do
+  class Projects < Grape::API
+    helpers Helpers::ProjectsHelpers
+  end
+end
+```
+
+Given this CE API `params`:
+
+```ruby
+module API
+  module Helpers
+    module ProjectsHelpers
+      extend ActiveSupport::Concern
+      extend Grape::API::Helpers
+
+      params :optional_project_params_ce do
+        # CE specific params go here...
       end
-    end
 
-    params :optional_params do
-      # CE specific params go here...
+      params :optional_project_params_ee do
+      end
 
-      use :optional_params_ee
+      params :optional_project_params do
+        use :optional_project_params_ce
+        use :optional_project_params_ee
+      end
     end
   end
 end
 
-API::MergeRequests.prepend(EE::API::MergeRequests)
+API::Helpers::ProjectsHelpers.prepend(EE::API::Helpers::ProjectsHelpers)
 ```
 
-And then we could override it in EE module:
+We could override it in EE module:
 
 ```ruby
 module EE
   module API
-    module MergeRequests
-      extend ActiveSupport::Concern
+    module Helpers
+      module ProjectsHelpers
+        extend ActiveSupport::Concern
 
-      prepended do
-        helpers do
-          params :optional_params_ee do
+        prepended do
+          params :optional_project_params_ee do
             # EE specific params go here...
           end
         end
@@ -600,9 +616,6 @@ module EE
 end
 ```
 
-This way, the only difference between CE and EE for that API file would be
-`prepend EE::API::MergeRequests`.
-
 #### EE helpers
 
 To make it easy for an EE module to override the CE helpers, we need to define