Adds a screenshot wallpaper method to WallpaperManagerService.

Bug: 29963541

Change-Id: If0a574004f8bddf1ba170587a8187253fe045ef4
diff --git a/bridge/src/android/view/IWindowManagerImpl.java b/bridge/src/android/view/IWindowManagerImpl.java
index 4e4da8b..49ab9f9 100644
--- a/bridge/src/android/view/IWindowManagerImpl.java
+++ b/bridge/src/android/view/IWindowManagerImpl.java
@@ -590,4 +590,9 @@
 
     @Override
     public void removeWallpaperInputConsumer() throws RemoteException {}
+
+    @Override
+    public Bitmap screenshotWallpaper() throws RemoteException {
+        return null;
+    }
 }