Update DreamOverlayService to work with Headless System User Mode.

The DreamOverlayService must run as part of the system user SystemUI
instance as the user-specific instance only has secondary components
enabled. As a result, the added overlay window must be set to show
for all users.

Test: atest DreamOverlayServiceTest#testSystemFlagShowForAllUsersSetOnWindow
Test: manual - verified overlay appears when dream shown in HSUM
Fixes: 283486171
Change-Id: I14d3335cb0d2a78780258300737f5d0dbe8d97e1

packages/SystemUI/AndroidManifest.xml

@@ -817,7 +817,8 @@
         <service
             android:name=".dreams.DreamOverlayService"
             android:enabled="false"
-            android:exported="true" />
+            android:exported="true"
+            android:singleUser="true" />
 
         <activity android:name=".keyguard.WorkLockActivity"
                   android:label="@string/accessibility_desc_work_lock"

packages/SystemUI/src/com/android/systemui/dreams/DreamOverlayService.java

@@ -283,6 +283,7 @@ public class DreamOverlayService extends android.service.dreams.DreamOverlayServ
 
         mWindow.clearFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
         mWindow.addFlags(WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE);
+        mWindow.addPrivateFlags(WindowManager.LayoutParams.SYSTEM_FLAG_SHOW_FOR_ALL_USERS);
         mWindow.requestFeature(Window.FEATURE_NO_TITLE);
         // Hide all insets when the dream is showing
         mWindow.getDecorView().getWindowInsetsController().hide(WindowInsets.Type.systemBars());

packages/SystemUI/tests/src/com/android/systemui/dreams/DreamOverlayServiceTest.java

@@ -16,6 +16,8 @@
 
 package com.android.systemui.dreams;
 
+import static android.view.WindowManager.LayoutParams.SYSTEM_FLAG_SHOW_FOR_ALL_USERS;
+
 import static com.google.common.truth.Truth.assertThat;
 
 import static org.mockito.ArgumentMatchers.any;
@@ -512,4 +514,23 @@ public class DreamOverlayServiceTest extends SysuiTestCase {
         mMainExecutor.runAllReady();
         verify(mDreamOverlayContainerViewController, never()).wakeUp(callback, mMainExecutor);
     }
+
+    @Test
+    public void testSystemFlagShowForAllUsersSetOnWindow() throws RemoteException {
+        final IDreamOverlayClient client = getClient();
+
+        // Inform the overlay service of dream starting. Do not show dream complications.
+        client.startDream(mWindowParams, mDreamOverlayCallback, DREAM_COMPONENT,
+                false /*shouldShowComplication*/);
+        mMainExecutor.runAllReady();
+
+        final ArgumentCaptor<WindowManager.LayoutParams> paramsCaptor =
+                ArgumentCaptor.forClass(WindowManager.LayoutParams.class);
+
+        // Verify that a new window is added.
+        verify(mWindowManager).addView(any(), paramsCaptor.capture());
+
+        assertThat((paramsCaptor.getValue().privateFlags & SYSTEM_FLAG_SHOW_FOR_ALL_USERS)
+                == SYSTEM_FLAG_SHOW_FOR_ALL_USERS).isTrue();
+    }
 }