Snapshot 2 tasks when swipe up split case

Swipe up snapshot only capture the top one task, but for split
screen case it should capture two tasks otherwise the snapshot
in overview would be empty in some cases.

Fix: 247420799
Test: manual
Test: pass existing tests
Change-Id: I3acd477eaca3cb98d86e2446dbb2dbd6295c687d
1 file changed