cache strings in the AST for faster comparison than include?

actionpack/lib/action_dispatch/middleware/static.rb

@@ -35,18 +35,15 @@ module ActionDispatch
   end
 
   class Static
-    FILE_METHODS = %w(GET HEAD).freeze
-
     def initialize(app, path, cache_control=nil)
       @app = app
       @file_handler = FileHandler.new(path, cache_control)
     end
 
     def call(env)
+      case env['REQUEST_METHOD']
+      when 'GET', 'HEAD'
         path = env['PATH_INFO'].chomp('/')
-      method = env['REQUEST_METHOD']
-
-      if FILE_METHODS.include?(method)
         if match = @file_handler.match?(path)
           env["PATH_INFO"] = match
           return @file_handler.call(env)