Update AS::Notifications::Instrumenter#instrument

  * Update #instrument to make passing a block optional. This will let users
    leverage #instrument for messaging in addition to instrumentation.

activesupport/lib/active_support/notifications/instrumenter.rb

@@ -20,7 +20,7 @@ def instrument(name, payload = {})
         # some of the listeners might have state
         listeners_state = start name, payload
         begin
-          yield payload
+          yield payload if block_given?
         rescue Exception => e
           payload[:exception] = [e.class.name, e.message]
           payload[:exception_object] = e

activesupport/test/notifications/instrumenter_test.rb

@@ -44,6 +44,12 @@ def test_instrument_yields_the_payload_for_further_modification
         assert_equal Hash[result: 2], payload
       end
 
+      def test_instrument_works_without_a_block
+        instrumenter.instrument("no.block", payload)
+        assert_equal 1, notifier.finishes.size
+        assert_equal "no.block", notifier.finishes.first.first
+      end
+
       def test_start
         instrumenter.start("foo", payload)
         assert_equal [["foo", instrumenter.id, payload]], notifier.starts