Add build stuck badge performance experiment

This commit adds a new feature flag that will be used to run an
experiment that will allow us to evaluate possible database peformance
improvement related to not running an expensive SQL query for every
runner in a project.

app/models/ci/build.rb

@@ -723,7 +723,13 @@ module Ci
     end
 
     def any_runners_online?
-      project.any_runners? { |runner| runner.active? && runner.online? && runner.can_pick?(self) }
+      project.any_runners? do |runner|
+        if Feature.enabled?(:ci_build_stuck_badge_performance_experiment, project, type: :development, default_enabled: false)
+          runner.active? && runner.online?
+        else
+          runner.active? && runner.online? && runner.can_pick?(self)
+        end
+      end
     end
 
     def stuck?

changelogs/unreleased/fix-gb-ci-build-stuck-badge-performance-experiment.yml

+---
+title: Add build stuck badge performance experiment
+merge_request: 50521
+author:
+type: performance

config/feature_flags/development/ci_build_stuck_badge_performance_experiment.yml

+---
+name: ci_build_stuck_badge_performance_experiment
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/50521
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/295490
+milestone: '13.7'
+type: development
+group: group::continuous integration
+default_enabled: false

spec/models/ci/build_spec.rb

@@ -580,9 +580,27 @@ RSpec.describe Ci::Build do
         is_expected.to be_falsey
       end
 
-      it 'that cannot handle build' do
-        expect_any_instance_of(Ci::Runner).to receive(:can_pick?).and_return(false)
-        is_expected.to be_falsey
+      context 'when runners are on-line but none can pick a build' do
+        before do
+          allow_any_instance_of(Ci::Runner)
+            .to receive(:can_pick?).and_return(false)
+        end
+
+        context 'when a performance experiement feature flag is enabled' do
+          before do
+            stub_feature_flags(ci_build_stuck_badge_performance_experiment: true)
+          end
+
+          it { is_expected.to be_truthy }
+        end
+
+        context 'when a performance experiment is not running' do
+          before do
+            stub_feature_flags(ci_build_stuck_badge_performance_experiment: false)
+          end
+
+          it { is_expected.to be_falsey }
+        end
       end
     end
   end