Notify SystemUI when ActivityDisplay is ready

Bug: 120748674
Test: atest ActivityManagerMultiDisplayTests#testNavBarNotShowingOnDisplayWithoutDecor * 100
Test: atest ActivityManagerMultiDisplayTests#testNavBarShowingOnDisplayWithDecor * 100
Test: atest ActivityManagerMultiDisplayTests#testNavBarNotShowingOnPrivateDisplay * 100
Test: atest SystemUITests
Change-Id: I302a35b9b860ab881b60c6407edabb2da16b75f8
diff --git a/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java b/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
index a66f0ca..b9b5aae 100644
--- a/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
+++ b/services/core/java/com/android/server/statusbar/StatusBarManagerInternal.java
@@ -100,4 +100,11 @@
      * @param rotation rotation suggestion
      */
     void onProposedRotationChanged(int rotation, boolean isValid);
+
+    /**
+     * Notifies System UI that the display is ready to show system decorations.
+     *
+     * @param displayId display ID
+     */
+    void onDisplayReady(int displayId);
 }