Merge pull request rails#27926 from st0012/freeze-cache-instrument-name

Freeze fragment cache related instrument name.

Author: rafaelfranca

actionmailer/lib/action_mailer/base.rb

@@ -972,7 +972,7 @@ def instrument_payload(key)
       end
 
       def instrument_name
-        "action_mailer"
+        "action_mailer".freeze
       end
 
       ActiveSupport.run_load_hooks(:action_mailer, self)

actionpack/lib/abstract_controller/caching/fragments.rb

@@ -136,7 +136,7 @@ def expire_fragment(key, options = nil)
 
       def instrument_fragment_cache(name, key) # :nodoc:
         payload = instrument_payload(key)
-        ActiveSupport::Notifications.instrument("#{name}.#{instrument_name}", payload) { yield }
+        ActiveSupport::Notifications.instrument("#{name}.#{instrument_name}".freeze, payload) { yield }
       end
     end
   end

actionpack/lib/action_controller/caching.rb

@@ -38,7 +38,7 @@ def instrument_payload(key)
       end
 
       def instrument_name
-        "action_controller"
+        "action_controller".freeze
       end
   end
 end