Redraw legacy navigation bar paint onLayout

Navigation bar background wasn't being redrawn
when using legacy navigation bar.

Fixes: 140096278
Test: Open Sheets app, turn landscape, select
a cell, press the "Fx" button on buttom left,
turn portrait and observe no black bar.
Open Sheets app, turn landscape, open recents
and select sheets icon and go into split screen,
choose any other app, click on cell, press "Fx",
turn portrait, observe no black bar.

Change-Id: Ibfe1abdba87a0d66c68478ee206b992c933cd9ad
(cherry picked from commit 7ab1fb8f37)

core/java/com/android/internal/policy/DecorView.java

@@ -796,7 +796,9 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         updateElevation();
         mAllowUpdateElevation = true;
 
-        if (changed && mResizeMode == RESIZE_MODE_DOCKED_DIVIDER) {
+        if (changed
+                && (mResizeMode == RESIZE_MODE_DOCKED_DIVIDER
+                    || mDrawLegacyNavigationBarBackground)) {
             getViewRootImpl().requestInvalidateRootRenderNode();
         }
     }