Frame token involves extra process hops and complicates the code so it should be avoided whenever possible. Frame token ensures that the parent doesn't get ahead of the child, but it can still fall behind. In fact, it will fall farther behind than if we weren't using frame token at all because of the delay caused by extra IPC. So unless getting ahead is considered worse than falling behind (which I don't think is the case for scroll data), I think we shouldn't use frame token.