[User Switcher] Finish activity when switch user

When switching to owner (user 0), we don't end up in lock screen like
when you switch to a secondary user. My belief is that this is because
the system user does not need to spin up a new process for system UI,
whereas a secondary user will need a secondary process.

We can keep the experience consistent by ensuring that the activity
finishes when a user is switched.

Bug: 228901638
Test: Manual Test
Change-Id: I74623655704cb89e499940498aef5a811dadf77e

packages/SystemUI/src/com/android/systemui/user/UserSwitcherActivity.kt

@@ -42,7 +42,7 @@ import com.android.systemui.R
 import com.android.systemui.broadcast.BroadcastDispatcher
 import com.android.systemui.plugins.FalsingManager
 import com.android.systemui.plugins.FalsingManager.LOW_PENALTY
-import com.android.systemui.statusbar.phone.ShadeController
+import com.android.systemui.settings.UserTracker
 import com.android.systemui.statusbar.policy.UserSwitcherController
 import com.android.systemui.statusbar.policy.UserSwitcherController.BaseUserAdapter
 import com.android.systemui.statusbar.policy.UserSwitcherController.USER_SWITCH_DISABLED_ALPHA
@@ -63,7 +63,7 @@ class UserSwitcherActivity @Inject constructor(
     private val layoutInflater: LayoutInflater,
     private val falsingManager: FalsingManager,
     private val userManager: UserManager,
-    private val shadeController: ShadeController
+    private val userTracker: UserTracker
 ) : LifecycleActivity() {
 
     private lateinit var parent: ViewGroup
@@ -215,6 +215,11 @@ class UserSwitcherActivity @Inject constructor(
         initBroadcastReceiver()
 
         parent.post { buildUserViews() }
+        userTracker.addCallback(object : UserTracker.Callback {
+            override fun onUserChanged(newUser: Int, userContext: Context) {
+                finish()
+            }
+        }, mainExecutor)
     }
 
     private fun showPopupMenu() {

packages/SystemUI/tests/src/com/android/systemui/user/UserSwitcherActivityTest.kt

@@ -24,7 +24,7 @@ import androidx.test.filters.SmallTest
 import com.android.systemui.SysuiTestCase
 import com.android.systemui.broadcast.BroadcastDispatcher
 import com.android.systemui.plugins.FalsingManager
-import com.android.systemui.statusbar.phone.ShadeController
+import com.android.systemui.settings.UserTracker
 import com.android.systemui.statusbar.policy.UserSwitcherController
 import com.google.common.truth.Truth.assertThat
 import org.junit.Before
@@ -50,7 +50,7 @@ class UserSwitcherActivityTest : SysuiTestCase() {
     @Mock
     private lateinit var userManager: UserManager
     @Mock
-    private lateinit var shadeController: ShadeController
+    private lateinit var userTracker: UserTracker
 
     @Before
     fun setUp() {
@@ -61,7 +61,7 @@ class UserSwitcherActivityTest : SysuiTestCase() {
             layoutInflater,
             falsingManager,
             userManager,
-            shadeController
+            userTracker
         )
     }