Remove redundant check

[marcoscaceres]

Closes #???

This check is not needed (or it's too eager because it's done on the wrong thread)... we do the check visibility check synchronously first.

There are rules already in place as to what to do if the visibility is lost after the lock is acquired.

The following tasks have been completed:

• Modified Web platform tests (link to pull request)

Implementation commitment:

• Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)
• WebKit (https://bugs.webkit.org/show_bug.cgi?id=)

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Preview | Diff

[vinhill]

I have some concerns about this check being necessary to prevent a race condition. While the task created in step 7.3 is still queued, the document could loose visibility, release all locks in document.[[ActiveLocks]]["screen"] and only afterwards, the task will run, acquire a new lock and place it in document.[[ActiveLocks]].

[marcoscaceres]

Yeah, that's true... theoretically that could happen. Let's leave this in place then.