Get rid of setZOrderOnTop for theme preview

To make the usage of warkspace and wallpaper surfaceview consistent in the app.

Test: Manually
Bug: 156321486
Change-Id: I66466d5b9f8797204842538fc4dd9b90a3be86e7
diff --git a/res/layout/grid_preview_card.xml b/res/layout/grid_preview_card.xml
index cdad6e9..2939f80 100644
--- a/res/layout/grid_preview_card.xml
+++ b/res/layout/grid_preview_card.xml
@@ -21,12 +21,6 @@
     android:layout_height="match_parent"
     android:layout_gravity="center">
 
-    <FrameLayout
-        android:id="@+id/grid_preview_container"
-        android:layout_width="match_parent"
-        android:layout_height="match_parent"
-        android:background="@color/primary_color" />
-
     <ImageView
         android:id="@+id/wallpaper_preview_image"
         android:layout_width="match_parent"
@@ -38,4 +32,8 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent" />
 
+    <FrameLayout
+        android:id="@+id/grid_preview_container"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent" />
 </androidx.cardview.widget.CardView>
\ No newline at end of file
diff --git a/src/com/android/customization/picker/grid/GridOptionPreviewer.java b/src/com/android/customization/picker/grid/GridOptionPreviewer.java
index cbe8ef2..6d31689 100644
--- a/src/com/android/customization/picker/grid/GridOptionPreviewer.java
+++ b/src/com/android/customization/picker/grid/GridOptionPreviewer.java
@@ -80,7 +80,7 @@
         if (usesSurfaceView) {
             mGridOptionSurface = new SurfaceView(mContext);
             setUpView(mGridOptionSurface);
-            mGridOptionSurface.setZOrderOnTop(true);
+            mGridOptionSurface.setZOrderMediaOverlay(true);
             mGridOptionSurface.getHolder().addCallback(mSurfaceCallback);
         } else {
             final ImageView previewImage = new ImageView(mContext);