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 a27bd3c8bf6e0d2575138592243cdb29d565bcf1..a8c01e240de7f5027e0db7cdf052b47a3fe90ab8 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -197,6 +197,19 @@ void AddClipNodeIfNeeded(const DataForRecursion<LayerType>& data_from_ancestor,
 }
 
 template <typename LayerType>
+static bool IsRootLayerOfNewRenderingContext(LayerType* layer) {
+  if (layer->parent())
+    return !layer->parent()->Is3dSorted() && layer->Is3dSorted();
+  return layer->Is3dSorted();
+}
+
+template <typename LayerType>
+static bool EndsExisiting3dRenderingContext(LayerType* layer) {
+  return layer->parent() ? layer->parent()->Is3dSorted() && !layer->Is3dSorted()
+                         : false;
+}
+
+template <typename LayerType>
 bool AddTransformNodeIfNeeded(
     const DataForRecursion<LayerType>& data_from_ancestor,
     LayerType* layer,
@@ -232,10 +245,16 @@ bool AddTransformNodeIfNeeded(
       layer->parent()->effect_tree_index() !=
           layer->scroll_parent()->effect_tree_index();
 
+  const bool is_root_of_new_rendering_context =
+      IsRootLayerOfNewRenderingContext(layer);
+  const bool ends_3d_rendering_context = EndsExisiting3dRenderingContext(layer);
+
   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_root_of_new_rendering_context ||
+                       ends_3d_rendering_context;
 
   LayerType* transform_parent = GetTransformParent(data_from_ancestor, layer);
   DCHECK(is_root || transform_parent);
@@ -312,6 +331,8 @@ bool AddTransformNodeIfNeeded(
   node->data.scrolls = is_scrollable;
   node->data.flattens_inherited_transform = data_for_children->should_flatten;
 
+  node->data.is_3d_sorted = layer->Is3dSorted();
+
   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 =