function measureTime(target, key, desc) {
  const fn = desc.value
  const { name } = fn

  desc.value = function(...args) {
    console.time(name)
    const result = fn.apply(this, ...args)
    console.timeEnd(name)
    return result
  }
}

// ...
class Editor {
  @measureTime
  onChange(nextState) {
    // Do something
  }
}