CSS Animations: Animations should start immediately when the page is not visible
CSS Animations: Animations should start immediately when the page is not visible

In r67865[1] the starting of CSS animations and transitions was deferred
until the next compositing update. This introduced a regression where
animations triggered on a page which is not visible would not start
until the page was made visible again.

This patch allows animations to start immediately when a page is not visible.

[1] https://src.chromium.org/viewvc/blink?view=rev&revision=167865

BUG=350892

Review URL: https://codereview.chromium.org/225093015

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@171021 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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