Merge "Revert "Switch "system/core/base" ref to "system/libbase""" am: ad5f9c3820 am: c454b59c16 am: a204141c1d

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1476116

Change-Id: I669a64798bb5706da1cb4431eba0e84be0637587