Method cloneBefore

lib/transition.js:181–185

* Add declaration if it is not exist

(decl, prop, value)

   * Add declaration if it is not exist
   */
  cloneBefore(decl, prop, value) {
    if (!this.already(decl, prop, value)) {
      decl.cloneBefore({ prop, value })
    }
  }

  /**
   * Check property for disabled by option