Handle nested position:sticky elements

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 375051ac04087affe87b921490b34eb9c0e83702..7508b87f0429481b9585fc56b4a2c1b211316a37 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -513,6 +513,19 @@ static inline bool ShouldFlattenTransform(LayerImpl* layer) {
   return layer->test_properties()->should_flatten_transform;
 }
 
+static inline gfx::Vector2dF CalculateTotalStickyOffsetToScroller(
+    LayerImpl* layer,
+    int scroll_ancestor_layer_id) {
+  return gfx::Vector2dF();
+}
+
+static inline gfx::Vector2dF CalculateTotalStickyOffsetToScroller(
+    Layer* layer,
+    int scroll_ancestor_layer_id) {
+  return draw_property_utils::CalculateTotalStickyOffsetToScroller(
+      layer, scroll_ancestor_layer_id);
+}
+
 template <typename LayerType>
 bool AddTransformNodeIfNeeded(
     const DataForRecursion<LayerType>& data_from_ancestor,
@@ -759,10 +772,32 @@ bool AddTransformNodeIfNeeded(
             .AddNodeAffectedByOuterViewportBoundsDelta(node->id);
       }
     }
-    sticky_data->main_thread_offset =
-        layer->position().OffsetFromOrigin() -
-        sticky_data->constraints.parent_relative_sticky_box_offset
-            .OffsetFromOrigin();
+
+    // The sticky box offset calculated in CompositedLayerMapping must be
+    // adjusted for the enclosing layer's scroll position and sticky offset.
+    // TODO(smcgruer): Maybe rename parent_relative_sticky_box_offset ?
+    gfx::Point sticky_box_offset(
+        sticky_data->constraints.parent_relative_sticky_box_offset);
+    if (Parent(layer)->id() != scroll_ancestor->owning_layer_id) {
+      sticky_box_offset -= gfx::ScrollOffsetToFlooredVector2d(
+          data_for_children->property_trees->scroll_tree.current_scroll_offset(
+              scroll_ancestor->owning_layer_id));
+      sticky_box_offset +=
+          gfx::ToFlooredVector2d(CalculateTotalStickyOffsetToScroller(
+              Parent(layer), scroll_ancestor->owning_layer_id));
+    }
+    sticky_data->main_thread_offset = layer->position().OffsetFromOrigin() -
+                                      sticky_box_offset.OffsetFromOrigin();
+    if (Layer* layer =
+            sticky_data->constraints.nearest_layer_shifting_sticky_box) {
+      sticky_data->nearest_node_shifting_sticky_box =
+          layer->transform_tree_index();
+    }
+    if (Layer* layer =
+            sticky_data->constraints.nearest_layer_shifting_containing_block) {
+      sticky_data->nearest_node_shifting_containing_block =
+          layer->transform_tree_index();
+    }
   }
 
   node->needs_local_transform_update = true;