Import jni_generator from root package am: 463ea434c7

Original change: https://android-review.googlesource.com/c/platform/external/libchrome/+/2237476

Change-Id: I5706b0a98206737579b1397809a99245c2b2b0a4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>