Use true present fence times in PowerHintSession duration calc am: c6b9d38c27 am: ce78d418ef

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/18976901

Change-Id: I1465f1820f3635404880a222df26d81820ec9cf7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>