DCHECK that property tree access is safe in LayerTreeImpl::DidUpdateScrollState

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 175c9a4f49f218506549699fdcf7e447153ab0aa..7f2d7994f404ae1991f618bd5c173bdc00849487 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -207,6 +207,8 @@ void LayerTreeImpl::DidUpdateScrollState(int layer_id) {
   if (!IsActiveTree())
     return;
 
+  DCHECK(lifecycle().AllowsPropertyTreeAccess());
+
   // The scroll_clip_layer Layer properties should be up-to-date.
   // TODO(pdr): This DCHECK fails on existing tests but should be enabled.
   // DCHECK(lifecycle().AllowsLayerPropertyAccess());