Unblock 'am start -W' if activity is brought to front without launching

If -W is used to start an activity successfully, but this activity just
brings another activity to front without actual launching, the waiting
will be stuck because neither activity will report launch complete.

In this case, we have to treat it as if the -W started an activity and
received return code START_TASK_TO_FRONT. It needs to wait for the new
activity to become visible (or report launch complete if it's already
visible).

This reverts earlier commits afb776d5,
since it's causing problems with launch time reporting.

bug: 28333487
bug: 29451567
Change-Id: I9fd79ab5b3ed8f9de5df34ed9c7b0be3a94620b2