Unshare mount namespace in bootchart's thread am: 1f85546b

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/17994482



Change-Id: I2a6351d338626f1487dbb94c1dff61a4d670b7b5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>