Add -XX:ForceJavaZygoteForkLoop flag

Setting this to true effectively disables the zygote native fork
loop, either for testing/measurement purposes, or as a fallback.

Bug: 192020504
Test: Check logcat with and without the flag.
Change-Id: I83c401d21ae2797442011d9ac6f23c78990920bd
Merged-In: I83c401d21ae2797442011d9ac6f23c78990920bd
(cherry picked from commit 1792c6ff1c9838dfbe948be124dc1a8501fc6636)
5 files changed