Polyfill ReadableStream on the devices that partially support it

[subhanahmed047]

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

Is your feature request related to a problem? Please describe.

While working on a promised PR for this issue on the Panasonic TV, after getting past the robustness problem, the player started throwing the NETWORK.UNSUPPORTED_SCHEME error.

Upon investigation, I realised that the http or https schemes are never registered on this TV. This means that this code never runs because shaka.net.HttpFetchPlugin.isSupported() returns false.

I can confirm that the TV has support for the following objects:
window.fetch => supported
window.ReadableStream => supported
window.AbortController => supported after Joey's Polyfill PR

The only thing is, the code

 new ReadableStream({});

throws an Uncaught TypeError: Illegal constructor error. Even tho the object is present.

Describe the solution you'd like

I was wondering if the Shaka player (if it doesn't already) can polyfill the ReadableStream to support it properly.

Additional context

This device uses chrome 49.
Polyfills are available for the ReadableStream such as this one.

[avelad]

Panasonic TV has xhr support? I say this because the fallback should be working.

On the other hand, the polyfill created by Joey doesn't work when network requests have to be aborted, see this: #4707 (comment)

[subhanahmed047]

@avelad where does it fall back to the XHR? Panasonic Does support XHR.

https://github.com/shaka-project/shaka-player/blob/main/lib/net/networking_engine.js/#L441-L442
at this point, the object and plugin are undefined. Also, the schemes_ object doesn't include any schemes. That makes me think it's not even falling back.

[subhanahmed047]

I've decided to polyfill the ReadableStream inside my app instead of asking Shaka to do it.