normalize_protocol

# File actionpack/lib/action_dispatch/http/url.rb, line 141
        def normalize_protocol(protocol)
          case protocol
          when nil
            "http://"
          when false, "//"
            "//"
          when PROTOCOL_REGEXP
            "#{$1}://"
          else
            raise ArgumentError, "Invalid :protocol option: #{protocol.inspect}"
          end
        end