Determine face orientation in (x, y: w) projected space

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index aa115f722648acc87a848bae40f36ff35eee9116..2fbbdc05dc846530b2167e9bfb99dfb22dcd49f5 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -327,41 +327,32 @@ static inline bool LayerIsInExisting3DRenderingContext(LayerType* layer) {
 }
 
 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 IsLayerBackFaceVisible(LayerType* layer) {
   // The current W3C spec on CSS transforms says that backface visibility should
   // be determined differently depending on whether the layer is in a "3d
-  // rendering context" or not. For Chromium code, we can determine whether we
-  // are in a 3d rendering context by checking if the parent preserves 3d.
-
-  if (LayerIsInExisting3DRenderingContext(layer))
+  // rendering context" or not.
+
+  // TODO(trchen): We should use the accumulated transform between the layer
+  // and the flattening layer (i.e. the parent of the root of the 3D-rendering
+  // context) to determine face orientation. Using draw transform works here
+  // because we make 3D-transformed flattening layer always creating a surface.
+  // Such requirement is not really necessary.
+  if (layer->Is3dSorted())
     return layer->draw_transform().IsBackFaceVisible();
 
-  // In this case, either the layer establishes a new 3d rendering context, or
-  // is not in a 3d rendering context at all.
+  // TODO(trchen): This is not entirely correct because the paint effect should
+  // include the perspective transform from parent element, which is provided
+  // in a separate layer.
   return layer->transform().IsBackFaceVisible();
 }
 
 template <typename LayerType>
 static bool IsSurfaceBackFaceVisible(LayerType* layer,
                                      const gfx::Transform& draw_transform) {
-  if (LayerIsInExisting3DRenderingContext(layer))
+  if (layer->Is3dSorted())
     return draw_transform.IsBackFaceVisible();
 
-  if (IsRootLayerOfNewRenderingContext(layer))
-    return layer->transform().IsBackFaceVisible();
-
-  // If the render_surface is not part of a new or existing rendering context,
-  // then the layers that contribute to this surface will decide back-face
-  // visibility for themselves.
-  return false;
+  return layer->transform().IsBackFaceVisible();
 }
 
 template <typename LayerType>