Thanks for your contribution. My comments are keep the bottom padding consistent with topPadding. Define a local variable and use it in the 2 places.

Also the scaffold shouldn't prevent its child from drawing under the home bar on iPhone X etc. Don't add the MediaQuery.padding.bottom to the scaffold padding.

I've just made this PR properly in a separate branch, so this got closed. I'll open a new one including your suggestions.
Regarding the addition of MediaQuery.padding.bottom, should I also modify current test with new value so it'll pass? (it failed in test/cupertino/scaffold_test.dart:116)

I meant we shouldn't add MediaQuery.padding.bottom to the padding of the scaffold's child. Imagine the child is a ListView with a black background, the list items would scroll in from above the home bar and there'd be a white gap at the bottom of the black screen.

I've just re-opened this as #20929.
I guess this should be implemented in a way similar to material's Scaffold, but sadly that's beyond my flutter knowledge for now ;(