Fix variable type mismatch.
Fix variable type mismatch.

uint64_t and size_t are not the same type on some Chromium platforms.

gfe-relnote: no behavior change. Not protected.
PiperOrigin-RevId: 281602900
Change-Id: Ibe1e4aa62860eb981df05a795d883821d93d13ef

google/quiche,google/quiche,google/quiche,google/quiche