message: always use uid when calling performance.mark (fix
diff: @@ -14,14 +14,18 @@ let uid = 0
  export function initMixin (Vue: Class<Component>) {
  Vue.prototype._init = function (options?: Object) {
  + const vm: Component = this
  + // a uid
  + vm._uid = uid++
  +
  /* istanbul ignore if */
  + let startTag, endTag
  if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
  - mark('vue-perf-init')
  + startTag = `vue-perf-init:${vm._uid}`
  + endTag = `vue-perf-end:${vm._uid}`
  + mark(startTag)
  }
  - const vm: Component = this
  - // a uid
  - vm._uid = uid++
  // a flag to avoid this being observed
  vm._isVue = true
  // merge options
  @@ -57,8 +61,8 @@ export function initMixin (Vue: Class<Component>) {
  /* istanbul ignore if */
  if (process.env.NODE_ENV !== 'production' && config.performance && mark) {
  vm._name = formatComponentName(vm, false)
  - mark('vue-perf-init-end')
  - measure(`${vm._name} init`, 'vue-perf-init', 'vue-perf-init-end')
  + mark(endTag)
  + measure(`${vm._name} init`, startTag, endTag)
  }
  if (vm.$options.el) {
  