Forcefully set system window tokens to fullscreen

We never defined the behavior of non-fullscreen system windows.

Bug: 214111660
Test: testMetricsMatchesLayoutOnWindowContext passed.
Change-Id: I9badcc975f25930258b48131a61b60fad089ba73

services/core/java/com/android/server/wm/WindowToken.java

@@ -16,6 +16,7 @@
 
 package com.android.server.wm;
 
+import static android.app.WindowConfiguration.WINDOWING_MODE_FULLSCREEN;
 import static android.view.WindowManager.LayoutParams.TYPE_DOCK_DIVIDER;
 import static android.view.WindowManager.LayoutParams.TYPE_NAVIGATION_BAR;
 
@@ -615,6 +616,12 @@ class WindowToken extends WindowContainer<WindowState> {
             getResolvedOverrideConfiguration().updateFrom(
                     mFixedRotationTransformState.mRotatedOverrideConfiguration);
         }
+        if (getTaskDisplayArea() == null) {
+            // We only defined behaviors of system windows in fullscreen mode, i.e. windows not
+            // contained in a task display area.
+            getResolvedOverrideConfiguration().windowConfiguration.setWindowingMode(
+                    WINDOWING_MODE_FULLSCREEN);
+        }
     }
 
     @Override