Select dependency linker based on file type

lib/gitlab/dependency_linker/base_linker.rb

 module Gitlab
   module DependencyLinker
     class BaseLinker
-      def self.link(plain_text, highlighted_text)
-        new(plain_text, highlighted_text).link
+      class_attribute :file_type
+
+      def self.support?(blob_name)
+        Gitlab::FileDetector.type_of(blob_name) == file_type
+      end
+
+      def self.link(*args)
+        new(*args).link
       end
 
       attr_accessor :plain_text, :highlighted_text

lib/gitlab/dependency_linker/gemfile_linker.rb

 module Gitlab
   module DependencyLinker
     class GemfileLinker < BaseLinker
-      def self.support?(blob_name)
-        blob_name == 'Gemfile' || blob_name == 'gems.rb'
-      end
+      self.file_type = :gemfile
 
       private
 

lib/gitlab/file_detector.rb

@@ -12,6 +12,7 @@ module Gitlab
       version: 'version',
       gitignore: '.gitignore',
       koding: '.koding.yml',
+      gemfile: /\A(Gemfile|gems\.rb)\z/,
       gitlab_ci: '.gitlab-ci.yml',
       avatar: /\Alogo\.(png|jpg|gif)\z/,
       route_map: 'route-map.yml'