def generate_stylesheets
      return @contents = Jammit.packager.pack_stylesheets(@package, @variant) unless @variant == :mhtml
      @mtime      = Time.now
      request_url = prefix_url(request.fullpath)
      cached_url  = prefix_url(Jammit.asset_url(@package, @extension, @variant, @mtime))
      css         = Jammit.packager.pack_stylesheets(@package, @variant, request_url)
      @contents   = css.gsub(request_url, cached_url) if perform_caching
      css
    end
def generate_stylesheets
      return @contents = Jammit.packager.pack_stylesheets(@package, @variant) unless @variant == :mhtml
      @mtime      = Time.now
      request_url = prefix_url(request.fullpath)
      cached_url  = prefix_url(Jammit.asset_url(@package, @extension, @variant, @mtime))
      css         = Jammit.packager.pack_stylesheets(@package, @variant, request_url)
      @contents   = css.gsub(request_url, cached_url) if perform_caching
      css
    end
If we're generating MHTML/CSS, return a stylesheet with the absolute
 request URL to the client, and cache a version with the timestamped cache
 URL swapped in.