Check for multi-window mode in AppTaskTests and ActivityManagerTest.

Some form factors may force tasks into multi-window mode and previous activities may remain visible in that case.

Fix: 350087414
Bug: 350079583
Change-Id: I8fa2aaa0af34665a9c9c1f59b2f3aa70c69a6bfc
Test: AppTaskTests ActivityManagerTest
Flag: TEST_ONLY
4 files changed