WebShare: Introduce web-share feature policy

[chromium-wpt-export-bot]

share() requests fail with a rejected promise if the 'web-share'
feature is not enabled.

We define 'self' as the default feature policy for web-share.

The spec has been updated
w3c/web-share#166

Intent to Ship
https://groups.google.com/a/chromium.org/g/blink-dev/c/fgme9KOd8CU/m/TCYPKQAXAwAJ

Bug: 1079104
Change-Id: Id4030448a54589eddb45185cbd6fd8970aee34c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2299791
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789872}

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.

[marcoscaceres]

@ericwilligers (@foolip maybe) I can't figure out what to do about the two CI fails above. One seems to be legit in crashing Chrome with these tests.

[ewilligers]

@ericwilligers (@foolip maybe) I can't figure out what to do about the two CI fails above. One seems to be legit in crashing Chrome with these tests.

The Chrome change hasn't landed yet.

Chrome doesn't currently have a share service implementation on non-Android platforms, so on desktop platforms navigator.share(...) will crash if navigator.share is enabled by flags or command line arguments, and the share doesn't reject with an exception due to permissions or types.

[marcoscaceres]

Ok, makes sense... @foolip, do you know if we can override the above tho? I'd like to land this so I have at least a test for the Gecko side. https://phabricator.services.mozilla.com/D84121

[ewilligers]

I have updated the test so existing desktop Chrome fails with a TypeError instead of a crash.

[foolip]

Ok, makes sense... @foolip, do you know if we can override the above tho?

This is already merged, but yes, it is possible to override failing CI checks with admin powers. When needed, you can ping me or someone else listed in https://web-platform-tests.org/admin/