Change default allowlist to 'all'

[nondebug]

Closes #155

The following tasks have been completed:

• [x] Modified Web platform tests (link to pull request)

Implementation commitment:

• [ ] WebKit (https://bugs.webkit.org/show_bug.cgi?id=230136)
• [ ] Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• [x] Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=)

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[marcoscaceres]

Linked Webkit bug... I'll see if I can quickly add it.

[marcoscaceres]

I... think the tests were actually testing 'all', by the looks of it.

[nondebug]

Actually, I think the tests expect that cross-origin access will be blocked by default. I uploaded a fix: https://crrev.com/c/3566254