Move finding of contributing file from tree to repository.

app/models/repository.rb

@@ -197,7 +197,12 @@ class Repository
   end
 
   def contribution_guide
-    cache.fetch(:contribution_guide) { tree(:head).contribution_guide }
+    cache.fetch(:contribution_guide) do
+      tree(:head).blobs.find do |file|
+        file.contributing?
+      end
+    end
+  end
   end
 
   def head_commit

app/models/tree.rb

 class Tree
   include Gitlab::MarkdownHelper
 
-  attr_accessor :entries, :readme, :contribution_guide
+  attr_accessor :entries, :readme
 
   def initialize(repository, sha, path = '/')
     path = '/' if path.blank?
@@ -28,11 +28,6 @@ class Tree
       readme_path = path == '/' ? readme_tree.name : File.join(path, readme_tree.name)
       @readme = Gitlab::Git::Blob.find(git_repo, sha, readme_path)
     end
-
-    if contribution_tree = @entries.find(&:contributing?)
-      contribution_path = path == '/' ? contribution_tree.name : File.join(path, contribution_tree.name)
-      @contribution_guide = Gitlab::Git::Blob.find(git_repo, sha, contribution_path)
-    end
   end
 
   def trees