Adjust MathML tests to Workaround WebKit's bug with document.fonts.ready

[fred-wang]

cc @mrego cc @youennf

That seems to be an acceptable work around to me. WDYT?

See also https://bugs.webkit.org/show_bug.cgi?id=183628

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Build PASSED

Started: 2018-03-14 14:38:57
Finished: 2018-03-14 14:47:04

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[mrego]

I think it's usually preferred window.requestAnimationFrame() instead of setTimeout().
Could you try if something like that would fix the issue? Thanks!

[fred-wang]

The WebKit bug is that document.fonts.ready resolves immediately, even when I replace the CSS @font-face with a list of document.fonts.add(...) just before document.fonts.ready. Using setTimeout or requestAnimationFrame will delay things a bit and hence solve the issue, but I'm not sure requestAnimationFrame is more appropriate here, since it's not really a layout/painting issue but a font API bug. For example the following changes do not allow to workaround the issue:

document.fonts.ready.then(() => { requestAnimationFrame(runTests); });

or
document.fonts.ready.then(() => { setTimeout(runTests, notSmallEnoughDelta); });

[mrego]

I was thinking in something like:

    window.requestAnimationFrame(() => { document.fonts.ready.then(runTests); });

However I agree with you that setTimeout() might be clearer, so I'm fine with keeping it.

[fred-wang]

Yes, requestAnimationFrame(() => { document.fonts.ready.then(runTests); }); would work too.

[mrego]

LGTM