Because there is no other options for 'None' or 'Swipe, there is no
necessary for showing the gear icon to show options.
'Lock screen message' could be found in
Settings > Display > Lock screen display.
Add testcase to verify the ChangeScreenLockPreferenceController's
behavior.
Test: make ROBOTEST_FILTER=ChangeScreenLockPreferenceControllerTest \
RunSettingsRoboTests -j40
Change-Id: Icdcd672261749d106162053d6f5228cee420a810
Fixes: 110848852
c2b6764057