Cache project branches and tags into variables

CHANGELOG

@@ -15,6 +15,7 @@ v 7.10.0 (unreleased)
   - Improve error message when save profile has error.
   - Passing the name of pushed ref to CI service (requires GitLab CI 7.9+)
   - Add location field to user profile
+  - Improve GitLab performance when working with git repositories
 
 v 7.9.0 (unreleased)
   - Add HipChat integration documentation (Stan Hu)

app/models/repository.rb

@@ -62,24 +62,28 @@ class Repository
 
   def add_branch(branch_name, ref)
     cache.expire(:branch_names)
+    @branches = nil
 
     gitlab_shell.add_branch(path_with_namespace, branch_name, ref)
   end
 
   def add_tag(tag_name, ref, message = nil)
     cache.expire(:tag_names)
+    @tags = nil
 
     gitlab_shell.add_tag(path_with_namespace, tag_name, ref, message)
   end
 
   def rm_branch(branch_name)
     cache.expire(:branch_names)
+    @branches = nil
 
     gitlab_shell.rm_branch(path_with_namespace, branch_name)
   end
 
   def rm_tag(tag_name)
     cache.expire(:tag_names)
+    @tags = nil
 
     gitlab_shell.rm_tag(path_with_namespace, tag_name)
   end
@@ -368,6 +372,18 @@ class Repository
     end
   end
 
+  def branches
+    @branches ||= raw_repository.branches
+  end
+
+  def tags
+    @tags ||= raw_repository.tags
+  end
+
+  def root_ref
+    @root_ref ||= raw_repository.root_ref
+  end
+
   private
 
   def cache