animationFrameRunner = function () {
            animFrameRequested = false;
            CURRENT_QUEUE = NEXT_QUEUE;
            NEXT_QUEUE = [];
            inAnimationFrameRunner = true;
            while (CURRENT_QUEUE.length > 0) {
                CURRENT_QUEUE.sort(AnimationFrameQueueItem.sort);
                var top_1 = CURRENT_QUEUE.shift();
                top_1.execute();
            }
            inAnimationFrameRunner = false;
        }
A flag to indicate if currently handling a native requestAnimationFrame callback