Native controls can hide/show captions, but not start them streaming

[joeyparrish]

Have you read the FAQ and checked for duplicate open issues?: Yes

What version of Shaka Player are you using?: v2.3.3

Can you reproduce the issue with our latest release version?: yes

Can you reproduce the issue with the latest code from master?: yes

Are you using the demo app or your own custom app?: demo

What browser and OS are you using?: Chrome 64 Linux

What did you do?

1. Open https://shaka-player-demo.appspot.com/demo/#asset=//storage.googleapis.com/shaka-demo-assets/angel-one/dash.mpd;lang=en-US;nativecontrols;build=uncompiled
2. Try to enable captions using the native video controls

What did you expect to happen? Captions show

What actually happened? Captions are "shown", but no cues exist because we aren't streaming them.

Present in v2.3.0, but not v2.2.10. I suspect this started with the implementation of #1058.

We no longer stream text content until the user asks us to show it, but that is connected through player.setTextTrackVisibility(), which is only called by custom controls. The captions button in the native video controls will show/hide captions, but not trigger the player to stream them.

[joeyparrish]

There does not appear to be an event to tell us when the native controls have been used to change the text track mode: https://html.spec.whatwg.org/multipage/media.html#texttrack

Perhaps we could add a configuration option, such that if enabled, we would stream regardless of text track state, as we used to do. With this option enabled, native controls could be used with text. Our demo app could set this option when native controls are toggled in the UI.

[joeyparrish]

I think I closed this too soon. The new configuration still needs to be used by the demo app.

[joeyparrish]

Cherry-picked for v2.3.4.