At blink side, overscroll is handled as part of rootscroller callback at the top of scroll-chain. If we cut off the scroll-chain by scroll-boundary-behavior, there would be no overscroll effect.

However at cc side, overscroll is handled in InputHandlerProxy outside scroll-chain, which means, even we have scroll-boundary-behavior cut off scroll-chain, we still have overscroll effect if there is any unconsumed delta.

We should handle the cc-side overscroll same with blink-side, by handling it at the top of the scroll-chain, so the scroll-boundary-behavior logic is more coherent.