cronet: Fix MissingNullability API linter errors am: 0ace420204

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2437174

Change-Id: Ifa80d96be2445ba2de067d65af9238ac733a67a9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>