Handle nested position:sticky elements

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 3446f38d659eca9b59008e00b341ce81d6f840f6..e8d361d3399de393ef6a9a96937db2335365640c 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -29,6 +29,7 @@
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/mutable_properties.h"
 #include "cc/trees/mutator_host.h"
+#include "cc/trees/scroll_node.h"
 #include "cc/trees/transform_node.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ -584,10 +585,39 @@ void Layer::SetPosition(const gfx::PointF& position) {
       StickyPositionNodeData* sticky_data =
           property_trees->transform_tree.StickyPositionData(
               transform_tree_index());
+      gfx::Point sticky_box_offset(
+          sticky_data->constraints.parent_relative_sticky_box_offset);
+
+      // 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 ?

[smcgruer, 2017/02/14 17:02:06]

flackr : Thoughts on renaming this?

+      ScrollNode* scroll_ancestor =
+          property_trees->scroll_tree.Node(scroll_tree_index());
+      if (scroll_ancestor->owning_layer_id == id()) {
+        // We are a scroller, so we need our parent's scroll_ancestor instead.
+        scroll_ancestor =
+            property_trees->scroll_tree.Node(parent()->scroll_tree_index());
+      }
+      if (parent()->id() != scroll_ancestor->owning_layer_id) {
+        sticky_box_offset -= gfx::ScrollOffsetToFlooredVector2d(
+            property_trees->scroll_tree.current_scroll_offset(
+                scroll_ancestor->owning_layer_id));
+        sticky_box_offset += gfx::ToFlooredVector2d(
+            draw_property_utils::CalculateTotalStickyOffsetToScroller(
+                parent(), scroll_ancestor->owning_layer_id));
+      }
       sticky_data->main_thread_offset =
-          position.OffsetFromOrigin() -
-          sticky_data->constraints.parent_relative_sticky_box_offset
-              .OffsetFromOrigin();
+          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();
+      }
     }
     transform_node->needs_local_transform_update = true;
     transform_node->transform_changed = true;