playbackRate custom values doesn't respect current speed

[bhenderson]

Description

playbackIndex is preset to 1, regardless of playbackValues passed in.

Expected Behavior

If I set playbackValues to [1,2,4,8], and the media playback rate is 1, clicking the button should change to 2

Actual Behavior

The playback rate is set to 4

I recognize that the current playback rate of the media might not be a provided option. I'm not sure what to do in that case. Probably just default to 0.