anchor.diff:    bool _maybeAddEventToFrame(TimelineEvent event, TimelineFrame frame) {
       assert(frame.isWellFormed);
   
  -    // TODO(kenzie): consider trimming VSYNC layer from pipelineProduceFlow. It
  -    // can start outside of the frame's time boundaries and could pose a risk
  -    // for us missing a frame.
  -
       // Ensure the event fits within the frame's time boundaries.
       if (!_eventOccursWithinFrameBoundaries(event, frame)) {
         return false;
  
positive.code:     // do event times extend slightly beyond the times we get from frame start
      // and end flow events.
  
      // Epsilon in microseconds.
      const int epsilon = 50;
  
      // Allow the event to extend the frame boundaries by [epsilon] microseconds.
      final bool fitsStartBoundary = f.startTime - e.startTime - epsilon < 0;
  
negative.code:   void _maybeAddCompletedFrame(TimelineFrame frame) {
      if (frame.isReadyForTimeline && frame.addedToTimeline == null) {
        _frameCompleteController.add(frame);
        _pendingFrames.remove(frame.id);
        frame.addedToTimeline = true;
      }
    }
  