Fix shared dim layer not cleared when all users removed

For secondary display, shared fullscreen dim layer user is
the only stack that is present on the display. When this stack
is removed the shared dim layer was not cleared. Because of
that it was crashing when trying to obtain DisplayContent from it.

Now when we're removing a dim layer user we check if we've removed
the last one and clear shared fullscreen dim layer if needed.

Bug: 34367817
Test: bit FrameworksServicesTests:com.android.server.wm.DimLayerControllerTests
Change-Id: I415196a345c491eddd26a55370bb819ce6485151
diff --git a/services/tests/servicestests/src/com/android/server/wm/DisplayContentTests.java b/services/tests/servicestests/src/com/android/server/wm/DisplayContentTests.java
index e54e319..30f99e5 100644
--- a/services/tests/servicestests/src/com/android/server/wm/DisplayContentTests.java
+++ b/services/tests/servicestests/src/com/android/server/wm/DisplayContentTests.java
@@ -29,6 +29,7 @@
 
 import java.util.ArrayList;
 
+import static android.view.Display.DEFAULT_DISPLAY;
 import static android.view.DisplayAdjustments.DEFAULT_DISPLAY_ADJUSTMENTS;
 import static android.view.WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
 import static android.view.WindowManager.LayoutParams.TYPE_VOICE_INTERACTION;
@@ -215,13 +216,8 @@
      */
     @Test
     public void testMoveStackBetweenDisplays() throws Exception {
-        // Create second display.
-        final Display display = new Display(DisplayManagerGlobal.getInstance(),
-                sDisplayContent.getDisplayId() + 1, new DisplayInfo(),
-                DEFAULT_DISPLAY_ADJUSTMENTS);
-        final DisplayContent dc = new DisplayContent(display, sWm, sLayersController,
-                new WallpaperController(sWm));
-        sWm.mRoot.addChild(dc, 1);
+        // Create a second display.
+        final DisplayContent dc = createNewDisplay();
 
         // Add stack with activity.
         final TaskStack stack = createTaskStackOnDisplay(dc);
@@ -261,10 +257,31 @@
 
         // Check that override config is applied.
         assertEquals(newOverrideConfig, sDisplayContent.getOverrideConfiguration());
+    }
+
+    /**
+     * This tests global configuration updates when default display config is updated.
+     */
+    @Test
+    public void testDefaultDisplayOverrideConfigUpdate() throws Exception {
+        final Configuration currentOverrideConfig = sDisplayContent.getOverrideConfiguration();
+
+        // Create new, slightly changed override configuration and apply it to the display.
+        final Configuration newOverrideConfig = new Configuration(currentOverrideConfig);
+        newOverrideConfig.densityDpi += 120;
+        newOverrideConfig.fontScale += 0.3;
+
+        sWm.setNewDisplayOverrideConfiguration(newOverrideConfig, DEFAULT_DISPLAY);
 
         // Check that global configuration is updated, as we've updated default display's config.
-        final Configuration globalConfig = sWm.mRoot.getConfiguration();
+        Configuration globalConfig = sWm.mRoot.getConfiguration();
         assertEquals(newOverrideConfig.densityDpi, globalConfig.densityDpi);
         assertEquals(newOverrideConfig.fontScale, globalConfig.fontScale, 0.1 /* delta */);
+
+        // Return back to original values.
+        sWm.setNewDisplayOverrideConfiguration(currentOverrideConfig, DEFAULT_DISPLAY);
+        globalConfig = sWm.mRoot.getConfiguration();
+        assertEquals(currentOverrideConfig.densityDpi, globalConfig.densityDpi);
+        assertEquals(currentOverrideConfig.fontScale, globalConfig.fontScale, 0.1 /* delta */);
     }
 }