vue2.1.7版本中，在vue/src/core/instance/init.js文件里出現(xiàn)如下代碼：

export function initMixin (Vue: Class<Component>) {
  Vue.prototype._init = function (options?: Object) {
    const vm: Component = this
    // a uid
    vm._uid = uid++
    // a flag to avoid this being observed
    vm._isVue = true
    // merge options
    if (options && options._isComponent) {
      // optimize internal component instantiation
      // since dynamic options merging is pretty slow, and none of the
      // internal component options needs special treatment.
      initInternalComponent(vm, options)
    } else {
      vm.$options = mergeOptions(
        resolveConstructorOptions(vm.constructor),
        options || {},
        vm
      )
    }
    /* istanbul ignore else */
    if (process.env.NODE_ENV !== 'production') {
      initProxy(vm)
    } else {
      vm._renderProxy = vm
    }
    // expose real self
    vm._self = vm
    initLifecycle(vm)
    initEvents(vm)
    callHook(vm, 'beforeCreate')
    initState(vm)
    callHook(vm, 'created')
    initRender(vm)
  }
}

在上述代碼中第一、二排中Vue: Class<Component>和(options?: Object)寫法是什么意思？