Merge "No need to 'addChild' when start 'FLAG_ACTIVITY_CLEAR_TOP' Activity." am: 5fa55ef1c8

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1553956

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Icb4e1456c4e6c93e75f4acc3bec04c76848d985f