Merge "simpleperf: improve help msg of --children in report cmd." am: bae691d7e6 am: 7e126f6b48 am: b3c4791e92

Original change: https://android-review.googlesource.com/c/platform/system/extras/+/1932820

Change-Id: Ia3d65b8eab2427d8f2ce6f0d6fc8e5e66e4b5fa5