The existing UiBlocker mechanism doesn't support additional visibility
control. With that, controllers that want to control their own
visibility won't be able to use UiBlocker.
Fixes: 223340393
Test: robotest
Change-Id: I2df2eb1ce77e2c94bb271a8b68cc8c6004df5c70
1. Don't create UiBlockerController if there is no related controller
2. Don't update visibility if UiBlockerController is null
3. Use findPreference() from DashboardFragment, which already has null
check.
Change-Id: Iee24c64317fb9d5a1cf2076d25728af485d390c5
Fixes: 122807414
Fixes: 122805831
Test: RunSettingsRoboTests
If DashboardFragment detects blocker controllers, it won't display
until:
1. All blocking controllers finish bg works.
2. Timeout
This CL adds UiBlockerController to control this behavior and
BlockingSlicePreferenceController as an example.
Bug: 120803703
Test: atest SettingsUnitTests
Change-Id: I66fc194776d46ee49b3ec7685f3167834e673ba2
