normalizePlugin (type, pluginRaw, pluginOptions = {}) {
    let plugin = this._pluginResolver.resolve(pluginRaw)
    if (!plugin.entry) {
      if (plugin.error) {
        logger.debug(plugin.error)
        throw new Error(`An error was encountered in ${type} "${pluginRaw}"`)
      } else {
        throw new Error(`Cannot resolve ${type} "${pluginRaw}"`)
      }
    }
    plugin = flattenPlugin(plugin, pluginOptions, this._pluginContext, this)
    plugin.$$normalized = true
    return plugin
  }
normalize plugin
@param pluginRaw
@param pluginOptions
@api public