Give the Desktop Mode owners ownership of DesktopModeFlags utility.

Change-Id: I3c0af0f76dee58d07cdc19ffeaa92db0b3b55c3d
diff --git a/core/java/android/window/OWNERS b/core/java/android/window/OWNERS
index 2c61df9..77c99b9 100644
--- a/core/java/android/window/OWNERS
+++ b/core/java/android/window/OWNERS
@@ -1,3 +1,5 @@
 set noparent
 
 include /services/core/java/com/android/server/wm/OWNERS
+
+per-file DesktopModeFlags.java = file:/libs/WindowManager/Shell/src/com/android/wm/shell/desktopmode/OWNERS