// The number of seconds the `step*` functions move the timeline.
*        The `Player` that this class should be attached to.
*        The key/value store of player options.
* attributes to whatever is passed in.
*        The percentage as a decimal that the bar should be filled from 0-1.
* Update the seek bar's UI.
*        The `timeupdate` or `ended` event that caused this to run.
* when player can't keep up.
* no matter what the actual internal values are. so we force it.
* Get the percentage of media played so far.
*         The percentage of media played so far (0 to 1).
*        The `mousedown` event that caused this to run.
*        The `mousemove` event that caused this to run.
// Don't let video end while scrubbing.
*        The `mouseup` event that caused this to run.
* default it will call `this.handleAction` when the key is space or enter.
* Call the update event for this Slider when this event happens on the player.