Add flag check to desktop multi instance UI.

Bug: 368554414
Test: Manual
Flag: com.android.window.flags.enable_desktop_windowing_multi_instance_features
Change-Id: I851f24c077d552527300329a0eae91dca85efa61
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecoration.java b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecoration.java
index 16036be..a264e17 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecoration.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecoration.java
@@ -984,7 +984,8 @@
         loadAppInfoIfNeeded();
         updateGenericLink();
         final boolean supportsMultiInstance = mMultiInstanceHelper
-                .supportsMultiInstanceSplit(mTaskInfo.baseActivity);
+                .supportsMultiInstanceSplit(mTaskInfo.baseActivity)
+                && Flags.enableDesktopWindowingMultiInstanceFeatures();
         final boolean shouldShowManageWindowsButton = supportsMultiInstance
                 && mMinimumInstancesFound;
         mHandleMenu = mHandleMenuFactory.create(