code: function start (startTiming) {
    if (isStart) {
      return
    }
    isStart = true
    recordTiming('MIPStart', startTiming)
    viewer.on('show', showTiming => {
      recordTiming('MIPPageShow', showTiming)
    })
  
    document.addEventListener('DOMContentLoaded', domLoaded, false)
    document.onreadystatechange = () => {
      if (document.readyState === 'complete') {
        domLoaded()
      }
    }
  }
docs: Start.
  
  @param {number} startTiming The MIP start timing.