End-to-end prototype of compositor scrolling with slimming paint v2

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 5a4a4c9d8935ade65c534242fc567184ab65d2bf..61f6b7e6ea52e67decbe50c24bbf6dfac80ec0c1 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -823,7 +823,8 @@ void Layer::SetScrollOffsetFromImplSide(
     property_trees->needs_rebuild = true;
 
   if (!inputs_.did_scroll_callback.is_null())
-    inputs_.did_scroll_callback.Run();
+    inputs_.did_scroll_callback.Run(scroll_offset);
+
   // The callback could potentially change the layer structure:
   // "this" may have been destroyed during the process.
 }