Reland Fade out overlay scrollbar after page load

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 33e17df36dbcd6eccc72e0f565d7195437c20185..253f398a36936e49a7d66b5c0e8eb87ab90e200c 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1694,6 +1694,9 @@ void LayerTreeImpl::RegisterScrollLayer(LayerImpl* layer) {
       std::pair<int, int>(layer->scroll_clip_layer_id(), layer->id()));
 
   DidUpdateScrollState(layer->id());
+
+  if (settings().scrollbar_animator == LayerTreeSettings::AURA_OVERLAY)
+    layer->set_needs_show_scrollbars(true);
 }
 
 void LayerTreeImpl::UnregisterScrollLayer(LayerImpl* layer) {