Update Firefox and Safari support for display-capture feature-policy

[lukewarlow]

Summary

This PR updates Firefox and Safari support for the display-capture feature policy. Also unmarks as experimental as it has at least 2 stable implementations.

Test results and supporting details

For Safari it's an educated guess based on the fact Safari implemented getDisplayMedia in Safari 13, and this commit which implements this feature was done in May 2019 which was before Safari 13 release.

I have also verified that it is at the very least implemented in Safari 14.1.

For the Firefox version, I tested with https://plastic-brief-carnation.glitch.me/ on browser stack and version 74 is when it worked as expected. I cannot find any mention of this in any Firefox release notes (I checked from version 67 onwards).

Tested on Firefox 92 and Safari 15 with https://demo.lukewarlow.uk/feature-policy/display-capture/ and can see that it doesn't support the header.

Firefox Android doesn't support get display media, and even when that's enabled (media.getdisplaymedia.enabled) it still doesn't actually work. So this feature policy can't be implemented in any meaningful way.

Related issues

Fixes #11554

Closes #12708

[eladalon1983]

Hello Luke,

I am still seeing incorrect data in MDN. Possibly the changes you've made have not gone live yet?

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For Safari it's an educated guess

Safari supports it as an iframe tag, but not as an HTTP header. I believe @youennf from Apple might be able to provide more information.

For the Firefox version, I tested with https://plastic-brief-carnation.glitch.me/ on browser stack and version 74 is when it worked as expected.

@jan-ivar might be able to help nail down the precise version.

For the Chrome version it's based on https://bugs.chromium.org/p/chromium/issues/detail?id=1150788 and taken the commit in the chromium release finder I get version 89. Verified for 92+.

Chrome supports display-capture starting with m94. Here is the CL, and here is Chrome's release schedule. You'll note that this made it to the branch cut of m94.

Thanks,
Elad

[lukewarlow]

It wont show yet because this MR hasn't been merged.

[lukewarlow]

I'm not personally going to add Chrome 94 support until it shows up in https://www.chromestatus.com/features/schedule

Unless a reviewer thinks it makes sense to do.

Any clarifications on the exact Firefox version would be welcome.

With regards to Safari if it doesn't work in the header I'll update it to partial support.

[eladalon1983]

I've updated the chromestatus.com entry for display-capture to reflect it's shipping in m94.

[lukewarlow]

Apologies didn't realise it was your changeset. 😆

[lukewarlow]

Have moved the Chrome related portion of this to #12526. As that's known good data.

[jan-ivar]

Safari supports it as an iframe tag, but not as an HTTP header.

Same in Firefox, even though Mozilla's position has softened a bit.

For the Firefox version, I tested with https://plastic-brief-carnation.glitch.me/ on browser stack and version 74 is when it worked as expected.

@jan-ivar might be able to help nail down the precise version.

This was enabled in 73.

[lukewarlow]

Thank you, have updated the PR with a note about only working on an allow attribute on iframes. Have made a follow up issue to address the other feature policy values being wrong for Firefox. However, this was actually enabled in version 74. See https://bugzilla.mozilla.org/show_bug.cgi?id=1617219. It appears it was aimed for 73 but backed out.

[ddbeck]

OK, this looks like it's ready. Thank you! 🎉