I worked at Google and have no idea what they mean by stacked change. You could push multiple changes to a single CL, but those were rarely reviewed independently.

Maybe they mean keeping a stack of CLs ready, while waiting for a review? I often had 1-2 CLs based on.. rebasing was fun sometimes.

Or they mean diffbasing these subsequent CLs, for an early review? That was useful, but due to volatility dependent on the first review, a bit risky.

Plug for a code review project: https://reviewpad.com/