old_contents: /* @flow */
  import Moment from 'moment';
  
  
  export type Poster = {
    key: string,
    title: string,
    authors: string,
    thumbnailUrl: string,
    savedAt: Moment,
  }
  
new_contents: /* @flow */
  import Moment from 'moment';
  
  
  export type Navigation = {
    navigate: Function,
    addListener: Function,
    removeListener: Function,
  };
  
  export type Poster = {
    key: string,
    title: string,
    authors: string,
    thumbnailUrl: string,
    savedAt: Moment,
  }
  
subject: Add Navigation type