Handle nested position:sticky elements correctly (compositor)

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 ef843d5d9890e67baba1396156fbca65bf06cb85..9c4866c2d97275c9c9ad1712bee2b098e5fa87a8 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -513,6 +513,20 @@ 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) {
+  NOTREACHED();
+  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 +773,29 @@ 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 sticky 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::ToFlooredVector2d(CalculateTotalStickyOffsetToScroller(
+              Parent(layer), scroll_ancestor->owning_layer_id));
+    }
+    sticky_data->main_thread_offset = layer->position().OffsetFromOrigin() -
+                                      sticky_box_offset.OffsetFromOrigin();
+    // Copy the ancestor nodes for later use. These layers are guaranteed to
+    // have transform nodes because they are our ancestors and they are sticky.
+    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;