Function prefixKey

docs/lib/react.js:481–483

* @param {string} prefix vendor-specific prefix, eg: Webkit * @param {string} key style name, eg: transitionDuration * @return {string} style name prefixed with `prefix`, properly camelCased, eg: * WebkitTransitionDuration

(prefix, key)

 * WebkitTransitionDuration
 */
function prefixKey(prefix, key) {
  return prefix + key.charAt(0).toUpperCase() + key.substring(1);
}

/**
 * Support style names that may come passed in prefixed by adding permutations