startTimer = () => {
  let startingTime

  try {
    startingTime = getMsTime()
  } catch (e) {
    return () => -1
  }

  return () => getMsTime() - startingTime
}
Returns a function that can be called again to find the time since the
function was instantiated.

Example:
```js
let timer = startTimer()
// undefined
timer()
// 15779.185
```

Returns -1 if browser didn't support performance API or Date API.