code: function mark (instance) {
    if (!instanceMap.has(instance.__VUE_DEVTOOLS_UID__)) {
      instanceMap.set(instance.__VUE_DEVTOOLS_UID__, instance)
      instance.$on('hook:beforeDestroy', function () {
        instanceMap.delete(instance.__VUE_DEVTOOLS_UID__)
      })
    }
  }
docs: Mark an instance as captured and store it in the instance map.
  
  @param {Vue} instance