Replace LayerImpl::sorting_context_id with transform reference.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 07af9251e79d2f3c029e8c336f0913b45a71aa18..0ef6fac86ed7c3101e9218a3387b552bb95392b7 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -75,7 +75,6 @@ LayerImpl::LayerImpl(LayerTreeImpl* tree_impl, int id)
       effect_tree_index_(EffectTree::kInvalidNodeId),
       clip_tree_index_(ClipTree::kInvalidNodeId),
       scroll_tree_index_(ScrollTree::kInvalidNodeId),
-      sorting_context_id_(0),
       current_draw_mode_(DRAW_MODE_NONE),
       mutable_properties_(MutableProperty::kNone),
       debug_info_(nullptr),
@@ -174,7 +173,7 @@ void LayerImpl::PopulateSharedQuadState(SharedQuadState* state) const {
   state->SetAll(draw_properties_.target_space_transform, bounds(),
                 draw_properties_.visible_layer_rect, draw_properties_.clip_rect,
                 draw_properties_.is_clipped, draw_properties_.opacity,
-                draw_blend_mode_, sorting_context_id_);
+                draw_blend_mode_, sorting_context_id());
 }
 
 void LayerImpl::PopulateScaledSharedQuadState(
@@ -194,7 +193,7 @@ void LayerImpl::PopulateScaledSharedQuadState(
   state->SetAll(scaled_draw_transform, scaled_bounds, scaled_visible_layer_rect,
                 draw_properties().clip_rect, draw_properties().is_clipped,
                 draw_properties().opacity, draw_blend_mode_,
-                sorting_context_id_);
+                sorting_context_id());
 }
 
 bool LayerImpl::WillDraw(DrawMode draw_mode,
@@ -357,7 +356,6 @@ void LayerImpl::PushPropertiesTo(LayerImpl* layer) {
   layer->effect_tree_index_ = effect_tree_index_;
   layer->clip_tree_index_ = clip_tree_index_;
   layer->scroll_tree_index_ = scroll_tree_index_;
-  layer->sorting_context_id_ = sorting_context_id_;
   layer->has_will_change_transform_hint_ = has_will_change_transform_hint_;
   layer->scrollbars_hidden_ = scrollbars_hidden_;
 
@@ -777,10 +775,6 @@ void LayerImpl::SetPosition(const gfx::PointF& position) {
   position_ = position;
 }
 
-void LayerImpl::Set3dSortingContextId(int id) {
-  sorting_context_id_ = id;
-}
-
 bool LayerImpl::TransformIsAnimating() const {
   return GetMutatorHost()->IsAnimatingTransformProperty(
       element_id(), GetElementTypeForAnimation());
@@ -1057,6 +1051,15 @@ bool LayerImpl::CanUseLCDText() const {
   return true;
 }
 
+int LayerImpl::sorting_context_id() const {
+  PropertyTrees* property_trees = layer_tree_impl()->property_trees();
+  return (!property_trees ||

[ajuma, 2017/01/06 14:59:55]

Looking at LayerTreeImpl::property_trees, I don't think this can ever be null.

[wkorman, 2017/01/06 22:50:02]

Done.

+          transform_tree_index() == TransformTree::kInvalidNodeId)

[ajuma, 2017/01/06 14:59:55]

This should never be kInvalidNodeId except in tests where we haven't built
property trees, and for those tests I think it'd be better to build property
trees (or remove the call to LayerImpl::sorting_context_id if it isn't essential
to the test).

[wkorman, 2017/01/06 22:50:02]

Done.

+             ? 0
+             : property_trees->transform_tree.Node(transform_tree_index())
+                   ->sorting_context_id;
+}
+
 Region LayerImpl::GetInvalidationRegionForDebugging() {
   return Region(update_rect_);
 }