Tests that page focus emulation is not reset by unrelated sessions
hasFocus(session1, before emulation):false
hasFocus(session2, before emulation):false
hasFocus(session1, after emulation):true
hasFocus(session2, after emulation):true
hasFocus(session1, after emulation, after session2 disconnect):true
hasFocus(session3, after emulation, after session1 disconnect):false