Add a way for wallpapers to know the delta between virtual screens.
diff --git a/core/java/android/view/ViewRoot.java b/core/java/android/view/ViewRoot.java
index f4593f5..bef3e58 100644
--- a/core/java/android/view/ViewRoot.java
+++ b/core/java/android/view/ViewRoot.java
@@ -2895,7 +2895,8 @@
             }
         }
         
-        public void dispatchWallpaperOffsets(float x, float y, boolean sync) {
+        public void dispatchWallpaperOffsets(float x, float y, float xStep, float yStep,
+                boolean sync) {
             if (sync) {
                 try {
                     sWindowSession.wallpaperOffsetsComplete(asBinder());