Google Calendar API：如何访问X-APPLE-TRAVEL-DURATION

Question

以.ics访问时，我的（Google）日历包含Apple日历旅行信息：

X-APPLE-TRAVEL-DURATION;VALUE=DURATION:PT45M

（完整示例here）

如何使用Google Calendar API检索此信息？ 列出事件时，不包括此信息。 E.g。

  {

   "kind": "calendar#event",
   "etag": "\"...\"",
   "id": "...",
   "status": "confirmed",
   "htmlLink": "https://www.google.com/calendar/event?eid=...",
   "created": "2016-05-29T11:45:53.000Z",
   "updated": "2016-05-29T11:45:53.530Z",
   "summary": "test apple travel",
   "creator": {
    "email": "john@doe.com",
    "displayName": "John Doe",
    "self": true
   },
   "organizer": {
    "email": "john@doe.com",
    "displayName": "John Doe",
    "self": true
   },
   "start": {
    "dateTime": "2016-05-30T13:00:00+02:00"
   },
   "end": {
    "dateTime": "2016-05-30T13:30:00+02:00"
   },
   "iCalUID": "...",
   "sequence": 0,
   "hangoutLink": "...",
   "reminders": {
    "useDefault": true
   }
  }