Handle nested position:sticky elements correctly (compositor)

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index c966f75f132a66ac259d56504e5e50b3ac9e336d..8f50bc93abe639de80c6231759291024fa2b4985 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"

[flackr, 2017/03/17 15:01:55]

Obsolete?

[smcgruer, 2017/03/17 17:36:51]

Done.

 #include "cc/trees/transform_node.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ -589,6 +590,8 @@ void Layer::SetPosition(const gfx::PointF& position) {
       StickyPositionNodeData* sticky_data =
           property_trees->transform_tree.StickyPositionData(
               transform_tree_index());
+      // This calculation will be incorrect if we have an ancestor sticky
+      // element that is not composited: http://crbug.com/702229

[flackr, 2017/03/17 15:01:55]

Can you change this to a TODO to either pass the main thread sticky shifting
offset of the non composited element or promote the ancestor sticky element?
i.e. suggests this will be fixed soon.

[smcgruer, 2017/03/17 17:36:51]

Done.

       sticky_data->main_thread_offset =
           position.OffsetFromOrigin() -
           sticky_data->constraints.parent_relative_sticky_box_offset