Merge branch 'instrument-api-helpers' into 'master'

Instrument all Grape API helpers

This has been added to help us figure out what's making certain Grape API calls slow (e.g. the one used for authorized keys as described in gitlab-com/operations#99).

See merge request !4169

CHANGELOG

@@ -57,6 +57,7 @@ v 8.8.0 (unreleased)
   - Redesign navigation for profile and group pages
   - Add counter metrics for rails cache
   - Import pull requests from GitHub where the source or target branches were removed
+  - All Grape API helpers are now instrumented
 
 v 8.7.6
   - Fix links on wiki pages for relative url setups. !4131 (Artem Sidorenko)

config/initializers/metrics.rb

@@ -118,6 +118,8 @@ if Gitlab::Metrics.enabled?
     # Instrument the classes used for checking if somebody has push access.
     config.instrument_instance_methods(Gitlab::GitAccess)
     config.instrument_instance_methods(Gitlab::GitAccessWiki)
+
+    config.instrument_instance_methods(API::Helpers)
   end
 
   GC::Profiler.enable