Avoid object creation during each frame

[simonla]

Choreographer.FrameCallback will be called each frame

We should avoid create new object here

There is no need to consider thread safety here, because it is guaranteed here and here

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[simonla]

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;
  }

[auto-submit[bot]]

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[auto-submit[bot]]

Validations Fail.

[simonla]

Validations Fail.

@jason-simmons help~ 👀

[dnfield]

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

[Hixie]

test-exempt: code refactor with no semantic change

[simonla]

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