I follow this methodology but I just ... use git? The hard part of making multiple small PRs is usually wrangling someone to actually review them, or following whatever process management has decided is necessary.
What's your git workflow for a change that depends on two other in flight changes? (More generally, of course, this can occur in an arbitrary part of one's change graph - which is usually not too deep, but at least in my experience, occasionally is.)
Having good tooling for this unlocked workflows I didn't know I was missing, and switching back to git when leaving Google felt like losing a limb.