Bug 270975 – Add ability to sniff media content should we failed to retrieve the content-type

• Status: RESOLVED
• Resolution: FIXED
• Component: Media

[Jean-Yves Avenard [:jya]]

We currently rely on the server to provide a valid content-type and if that fails we always use the URL's file name extension instead.

The HTML5 specs clearly states that the type of a resource should be determined through sniffing [1]

And that sniffing should take precedence over the supplied mime type [2].
Parsing the resource header [3] doing 
```
2. Read bytes of the resource into buffer until one of the following conditions is met:
  * the end of the resource is reached.
  * the number of bytes in buffer is greater than or equal to 1445.
  * a reasonable amount of time has elapsed, as determined by the user agent.
```

For now we will only rely on sniffing should the previous way of determining the content-type failed.

[1] https://html.spec.whatwg.org/#content-type-sniffing
[2] https://mimesniff.spec.whatwg.org/#rules-for-sniffing-audio-and-video-specifically
[3] https://mimesniff.spec.whatwg.org/#reading-the-resource-header

[Radar WebKit Bug Importer]

<rdar://problem/124614908>

[Jean-Yves Avenard [:jya]]

Pull request: https://github.com/WebKit/WebKit/pull/25883

[EWS]

Committed 276258@main (93f6303ff83e): <https://commits.webkit.org/276258@main>

Reviewed commits have been landed. Closing PR #25883 and removing active labels.

[Jean-Yves Avenard [:jya]]

likely the same as bug 245428