SIGN IN SIGN UP

Slightly improve comments in SliverMultiBoxAdaptorElement (#10939)

I got a bit confused by these comments when trying to debug this code,
let's try clearing them up a little.
I
Ian Hickson committed
59524c697b7904e915b6e7936bf4a6ea3b4b9426
Parent: df1a01b
Committed by GitHub <noreply@github.com> on 6/23/2017, 9:58:14 PM