tests for AnimationPlayer finished state

[alsemenov]

tests for AnimationPlayer finished state

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/1824

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[sideshowbarker]

@alsemenov you need to change the line endings in this test file

[sideshowbarker]

@birtles do you have time to review this over at https://critic.hoppipolla.co.uk/r/1824

[birtles]

Sorry, I think @dstockwell was going to look at this.

[sideshowbarker]

@alsemenov @birtles @dstockwell This PR has been waiting on review for almost 6 months now.

[birtles]

I'm going to close this PR unmerged because we have more focused and up-to-date tests in the tree already for this under web-animations/animation/finished.html and web-animations/animation/onfinish.html.