src: revamp internal field count tracking
Improved handling of internal field counts.
In a separate PR, it would likely be good to switch to use of utility functions that include DCHECK
s for the InternalFieldCount()
.
/cc @bnoordhuis @addaleax
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines