Make sure to pause activity before stopping

In some cases it is possible for activity manager to request
a resumed activity to stop when it's visibility changes. This
is a valid transition, however we need to make sure to pause
the activity on the client side before stopping it so lifecycle
transition works as expected.

Bug: 28574036
Change-Id: I759b38bbd1c9c3bb0475759bcb638d8223fa504d