System Bars: Ensure contrast when app requested transparent bar

Bug: 129533768
Test: atest EnsureBarContrastTest
Change-Id: Ib8f4045b9e8e7bf65c13437133f114d91d0cb050
diff --git a/packages/overlays/NavigationBarModeGesturalOverlay/res/values/config.xml b/packages/overlays/NavigationBarModeGesturalOverlay/res/values/config.xml
index 704ff2e..86fd47b 100644
--- a/packages/overlays/NavigationBarModeGesturalOverlay/res/values/config.xml
+++ b/packages/overlays/NavigationBarModeGesturalOverlay/res/values/config.xml
@@ -33,4 +33,8 @@
     <!-- Controls the size of the back gesture inset. -->
     <dimen name="config_backGestureInset">20dp</dimen>
 
+    <!-- Controls whether the navbar needs a scrim with
+     {@link Window#setEnsureNavigationBarContrastWhenTransparent}. -->
+    <bool name="config_navBarNeedsScrim">false</bool>
+
 </resources>