Add real to elapsed offset to shell transition trace am: 541c4b6021

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22988307

Change-Id: Iad589a9a728f164b8b94863888598115fd4eb26a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>