message: refactor(class-util): cache whitespace regex
diff: /* @flow */
  +const whitespaceRE = /\s+/
  +
  /**
  * Add class with compatibility for SVG since classList is not supported on
  * SVG elements in IE
  @@ -13,7 +15,7 @@ export function addClass (el: HTMLElement, cls: ?string) {
  /* istanbul ignore else */
  if (el.classList) {
  if (cls.indexOf(' ') > -1) {
  - cls.split(/\s+/).forEach(c => el.classList.add(c))
  + cls.split(whitespaceRE).forEach(c => el.classList.add(c))
  } else {
  el.classList.add(cls)
  }
  @@ -38,7 +40,7 @@ export function removeClass (el: HTMLElement, cls: ?string) {
  /* istanbul ignore else */
  if (el.classList) {
  if (cls.indexOf(' ') > -1) {
  - cls.split(/\s+/).forEach(c => el.classList.remove(c))
  + cls.split(whitespaceRE).forEach(c => el.classList.remove(c))
  } else {
  el.classList.remove(cls)
  }
  