Add wallpaper support to theme bundles

Show wallpaper preview if available, show a checkbox to keep the
current wallpaper and apply the theme's wallpaper if needed.

Bug: 120559294

Change-Id: I229ab6e3372ace8218356d965e8d38f074e95061
diff --git a/res/layout/fragment_theme_picker.xml b/res/layout/fragment_theme_picker.xml
index 245a22c..e20c5f9 100644
--- a/res/layout/fragment_theme_picker.xml
+++ b/res/layout/fragment_theme_picker.xml
@@ -45,6 +45,13 @@
         <RelativeLayout
             android:layout_width="match_parent"
             android:layout_height="wrap_content">
+            <CheckBox
+                android:id="@+id/use_my_wallpaper"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:layout_alignParentStart="true"
+                android:layout_centerVertical="true"
+                android:text="@string/keep_my_wallpaper"/>
             <Button
                 android:id="@+id/apply_button"
                 style="@style/ActionPrimaryButton"