cc:: Add transform nodes at boundaries of 3d rendering contexts

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index 8af9eb8a6c41a46666c8a4cc1438af6a0b59877a..1f9e6e376bea768cf1445c713f8040b535bfe6f3 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -232,10 +232,15 @@ bool AddTransformNodeIfNeeded(
       layer->parent()->effect_tree_index() !=
           layer->scroll_parent()->effect_tree_index();
 
+  const bool is_at_boundary_of_3d_rendering_context =
+      layer->parent()
+          ? layer->parent()->sorting_context_id() != layer->sorting_context_id()
+          : layer->Is3dSorted();
   bool requires_node = is_root || is_scrollable || has_significant_transform ||
                        has_any_transform_animation || has_surface || is_fixed ||
                        is_page_scale_layer || is_overscroll_elasticity_layer ||
-                       scroll_child_has_different_target;
+                       scroll_child_has_different_target ||
+                       is_at_boundary_of_3d_rendering_context;
 
   LayerType* transform_parent = GetTransformParent(data_from_ancestor, layer);
   DCHECK(is_root || transform_parent);
@@ -312,6 +317,8 @@ bool AddTransformNodeIfNeeded(
   node->data.scrolls = is_scrollable;
   node->data.flattens_inherited_transform = data_for_children->should_flatten;
 
+  node->data.sorting_context_id = layer->sorting_context_id();
+
   if (layer == data_from_ancestor.page_scale_layer)
     data_for_children->in_subtree_of_page_scale_layer = true;
   node->data.in_subtree_of_page_scale_layer =