Merge branch 'instrument-reference-parsers' into 'master'

Instrument all Banzai::ReferenceParser classes

## What does this MR do?

This MR instruments all the classes in the `Banzai::ReferenceParser` namespace.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

The classes in question weren't instrumented meaning we have no idea how they're performing in production.

## What are the relevant issue numbers?

None.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- [ ] ~~Tests~~
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4620

CHANGELOG

@@ -70,6 +70,7 @@ v 8.9.0 (unreleased)
   - Improved UX of date pickers on issue & milestone forms
   - Cache on the database if a project has an active external issue tracker.
   - Put project Labels and Milestones pages links under Issues and Merge Requests tabs as subnav
+  - All classes in the Banzai::ReferenceParser namespace are now instrumented
 
 v 8.8.5 (unreleased)
   - Ensure branch cleanup regardless of whether the GitHub import process succeeds

config/initializers/metrics.rb

@@ -96,14 +96,19 @@ if Gitlab::Metrics.enabled?
       config.instrument_instance_methods(const)
     end
 
-    # Instruments all Banzai filters
-    Dir[Rails.root.join('lib', 'banzai', 'filter', '*.rb')].each do |file|
+    # Instruments all Banzai filters and reference parsers
+    {
+      Filter: Rails.root.join('lib', 'banzai', 'filter', '*.rb'),
+      ReferenceParser: Rails.root.join('lib', 'banzai', 'reference_parser', '*.rb')
+    }.each do |const_name, path|
+      Dir[path].each do |file|
         klass = File.basename(file, File.extname(file)).camelize
-      const = Banzai::Filter.const_get(klass)
+        const = Banzai.const_get(const_name).const_get(klass)
 
         config.instrument_methods(const)
         config.instrument_instance_methods(const)
       end
+    end
 
     config.instrument_methods(Banzai::Renderer)
     config.instrument_methods(Banzai::Querying)