Implement position: sticky updates on compositor

cc/trees/property_tree.h

Index: cc/trees/property_tree.h
diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index 4f3a501cc20bf46b5538ee84d3875b78a3438c86..fe8382f65f7df5f9122475af94bb641135bd3c89 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -14,6 +14,7 @@
 #include "cc/animation/element_id.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/synced_property.h"
+#include "cc/layers/layer_sticky_position_constraint.h"
 #include "cc/output/filter_operations.h"
 #include "ui/gfx/geometry/rect_f.h"
 #include "ui/gfx/geometry/scroll_offset.h"
@@ -122,6 +123,14 @@ class CC_EXPORT PropertyTree {
   PropertyTrees* property_trees_;
 };
 
+struct StickyPositionNodeData {
+  int scroll_ancestor;
+  LayerStickyPositionConstraint constraints;
+  gfx::Vector2dF main_thread_offset;

[ajuma, 2016/09/08 22:08:54]

Please add a comment explaining what this represents. I think it's something
like the offset that Blink has applied to counteract the main thread scroll
offset of the scroll ancestor?

[flackr, 2016/09/20 17:08:13]

Done.

+
+  StickyPositionNodeData() : scroll_ancestor(-1) {}
+};
+
 class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
  public:
   TransformTree();
@@ -255,6 +264,9 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
     return cached_data_;
   }
 
+  StickyPositionNodeData* StickyPositionData(int node_id);
+  void SetNotSticky(int node_id);
+
   void ToProtobuf(proto::PropertyTree* proto) const;
   void FromProtobuf(const proto::PropertyTree& proto,
                     std::unordered_map<int, int>* node_id_to_index_map);
@@ -303,6 +315,8 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   std::vector<int> nodes_affected_by_inner_viewport_bounds_delta_;
   std::vector<int> nodes_affected_by_outer_viewport_bounds_delta_;
   std::vector<TransformCachedNodeData> cached_data_;
+  std::vector<StickyPositionNodeData> sticky_position_data_;
+  std::vector<int> sticky_position_data_free_ids_;
 };
 
 class CC_EXPORT ClipTree final : public PropertyTree<ClipNode> {