stringifyValue = function stringifyValue(key
/* : string */
, prop
/* : any */
)
/* : string */
{
  if (typeof prop === "number") {
    if (isUnitlessNumber[key]) {
      return "" + prop;
    } else {
      return prop + "px";
    }
  } else {
    return '' + prop;
  }
}
Support style names that may come passed in prefixed by adding permutations
of vendor prefixes.
Taken from React's CSSProperty.js