Implement position: sticky updates on compositor

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 6f076f525e32a09e1692cc135eee42603116def1..40dbb2ca226e4298d0bd401e91a8d5393b277368 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -611,6 +611,14 @@ void Layer::SetPosition(const gfx::PointF& position) {
     TransformNode* transform_node =
         property_trees->transform_tree.Node(transform_tree_index());
     transform_node->update_post_local_transform(position, transform_origin());
+    if (transform_node->sticky_position_constraint_id >= 0) {
+      StickyPositionNodeData* sticky_data =
+          property_trees->transform_tree.StickyPositionData(
+              transform_tree_index());
+      sticky_data->main_thread_offset =
+          position.OffsetFromOrigin() -
+          sticky_data->constraints.absolute_sticky_box_rect.OffsetFromOrigin();
+    }
     transform_node->needs_local_transform_update = true;
     transform_node->transform_changed = true;
     layer_tree_->property_trees()->transform_tree.set_needs_update(true);
@@ -1109,6 +1117,15 @@ void Layer::SetPositionConstraint(const LayerPositionConstraint& constraint) {
   SetNeedsCommit();
 }
 
+void Layer::SetStickyPositionConstraint(
+    const LayerStickyPositionConstraint& constraint) {
+  DCHECK(IsPropertyChangeAllowed());
+  if (inputs_.sticky_position_constraint == constraint)
+    return;
+  inputs_.sticky_position_constraint = constraint;
+  SetNeedsCommit();
+}
+
 static void RunCopyCallbackOnMainThread(
     std::unique_ptr<CopyOutputRequest> request,
     std::unique_ptr<CopyOutputResult> result) {
@@ -1167,6 +1184,7 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer->set_should_flatten_transform_from_property_tree(
       should_flatten_transform_from_property_tree_);
   layer->set_draw_blend_mode(draw_blend_mode_);
+  layer->SetStickyPositionConstraint(inputs_.sticky_position_constraint);
   layer->SetUseParentBackfaceVisibility(inputs_.use_parent_backface_visibility);
   layer->SetUseLocalTransformForBackfaceVisibility(
       use_local_transform_for_backface_visibility_);