Pretend to be having the original background

...as otherwise setWindowBackground(bg) => bg == dv.getBackground
property is violated.

Test: WindowTest
Fixes: 130170137
Change-Id: I21dc45b291fd2568355ff186966a910cd05ed994

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

@@ -627,7 +627,7 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
                 drawingBounds.bottom -= framePadding.bottom - frameOffsets.bottom;
             }
 
-            Drawable bg = getBackground();
+            Drawable bg = super.getBackground();
             if (bg != null) {
                 bg.setBounds(drawingBounds);
             }
@@ -1235,6 +1235,11 @@ public class DecorView extends FrameLayout implements RootViewSurfaceTaker, Wind
         mLastOriginalBackgroundDrawable = mOriginalBackgroundDrawable;
     }
 
+    @Override
+    public Drawable getBackground() {
+        return mOriginalBackgroundDrawable;
+    }
+
     private int calculateStatusBarColor() {
         return calculateBarColor(mWindow.getAttributes().flags, FLAG_TRANSLUCENT_STATUS,
                 mSemiTransparentBarColor, mWindow.mStatusBarColor);