It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

It looks like we will only have one request at same time

So we can hold one FrameCallback instance safely

animator.cc:

  if (!pending_frame_semaphore_.TryWait()) {
    // Multiple calls to Animator::RequestFrame will still result in a
    // single request to the VsyncWaiter.
    return;
  }

• Please get at least one approved review if you are already a member or two member reviews if you are not a member before re-applying this label. Reviewers: If you left a comment approving, please use the "approve" review action instead.

Validations Fail.

Validations Fail.

@jason-simmons help~ 👀

@simonla this needed a second reviewer, I've approved. Asking for a NTE from @Hixie

test-exempt: code refactor with no semantic change

@jason-simmons Got test-exempt and two approver. Would you mind helping me add the autosubmit tag again？