    # File lib/action_view/helpers/asset_tag_helper.rb, line 532
              def initialize(template, controller, source, include_host = true)
                # NOTE: The template arg is temporarily needed for a legacy plugin
                # hook that is expected to call rewrite_asset_path on the
                # template. This should eventually be removed.
                @template = template
                @controller = controller
                @source = source
                @include_host = include_host
                @cache_key = if controller.respond_to?(:request)
                  [self.class.name,controller.request.protocol,
                   ActionController::Base.asset_host,
                   ActionController::Base.relative_url_root,
                   source, include_host]
                else
                  [self.class.name,ActionController::Base.asset_host, source, include_host]
                end
              end