Add feature flag for tablesample counting.

lib/gitlab/database/count.rb

@@ -172,6 +172,10 @@ module Gitlab
           {}
         end
 
+        def self.enabled?
+          Gitlab::Database.postgresql? && Feature.enabled?(:tablesample_counts)
+        end
+
         private
         def perform_count(model, estimate)
           # If we estimate 0, we may not have statistics at all. Don't use them.

spec/lib/gitlab/database/count_spec.rb

@@ -163,6 +163,10 @@ describe Gitlab::Database::Count do
     end
 
     describe '.enabled?' do
+      before do
+        stub_feature_flags(tablesample_counts: true)
+      end
+
       it 'is enabled for PostgreSQL' do
         allow(Gitlab::Database).to receive(:postgresql?).and_return(true)