Webkit_pip polyfill breaks standard feature detection of PiP on iOS

[OrenMe]

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

What version of Shaka Player are you using?
2.5.5

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?
Own

If custom app, can you reproduce the issue using our demo app?
No, you need to have playsinline and you need to preform the standard check for is pictureInPicture as it is defined in various official guides like this:
if ('pictureInPictureEnabled' in document) {
For example in google chrome official docs https://developers.google.com/web/updates/2018/10/watch-video-using-picture-in-picture
And the code will return invalid result on iOS.
And the code that does it is in your polyfill for WebKit PiP here https://github.com/google/shaka-player/blob/7afac89bc2c53c6372e2fe30e4d2cba32fdb8e99/lib/polyfill/pip_webkit.js#L55 which shouldn’t get registered on iOS which doesn’t support PiP at all.
What happens is that our app has a button for PiP and it uses the standard feature detection and since we upgraded to 2.5.5(from a very old version) the button started showing in iOS due to the polyfill.

What browser and OS are you using?
iPhone safari ios13

For embedded devices (smart TVs, etc.), what model and firmware version are you using?

What are the manifest and license server URIs?

Any manifest will do

What did you do?

Try to check if shaka is supported or not on iOS

What did you expect to happen?
Shaka tells if it supported using its api but no other side effects

What actually happened?

The standard way to check if PiP is supported is broken due to side effects caused by the WebKit PiP polyfill

[ismena]

Let me see if I got the repro correctly, @OrenMe
Our check for PiP support gives a false-positive on iOS, where PiP is actually not supported.
Is that right?

We'd be happy to accept a PR for this, if you're up to it. Otherwise, we'll take a look.

[OrenMe]

Sure @ismena, I'll open a PR.

[joeyparrish]

The PR broke the PiP polyfill on desktop Safari. Apple's docs say that calling webkitSupportsPresentationMode on a video element with no video content loaded will always return false.

I will pursue another solution involving polyfilling the disablePictureInPicture attribute on the video element. If the polyfill is installed, it will show document.pictureInPictureEnabled==true, but video.disablePictureInPicture will be a getter that does a runtime check on that specific element using webkitSupportsPresentationMode.

disablePictureInPicture (JS property & HTML attribute) is part of the PiP spec, so this should be sufficient to disable PiP correctly on iOS in your application, whether or not you are using our UI.

[joeyparrish]

Cherry-picked to v2.5.9.