Expose Instrumenter id in Notifications.

activesupport/lib/active_support/notifications/instrumenter.rb

@@ -4,6 +4,8 @@ require 'active_support/core_ext/module/delegation'
 module ActiveSupport
   module Notifications
     class Instrumenter
+      attr_reader :id
+
       def initialize(notifier)
         @id = unique_id
         @notifier = notifier

activesupport/test/notifications_test.rb

@@ -86,6 +86,10 @@ module Notifications
       assert_equal 2, @notifier.instrument(:awesome) { 1 + 1 }
     end
 
+    def test_instrumenter_exposes_its_id
+      assert_equal 20, ActiveSupport::Notifications::Instrumenter.new(@notifier).id.size
+    end
+
     def test_nested_events_can_be_instrumented
       @notifier.instrument(:awesome, :payload => "notifications") do
         @notifier.instrument(:wot, :payload => "child") do