Implement position: sticky updates on compositor

cc/layers/layer.h

Index: cc/layers/layer.h
diff --git a/cc/layers/layer.h b/cc/layers/layer.h
index 762a56ce96f27fbb9f96bf8afec3103f9169b719..02240014219a5b5f9b64516c8651f19fe4aee387 100644
--- a/cc/layers/layer.h
+++ b/cc/layers/layer.h
@@ -191,6 +191,12 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
     return inputs_.position_constraint;
   }
 
+  void SetStickyPositionConstraint(
+      const LayerStickyPositionConstraint& constraint);
+  const LayerStickyPositionConstraint& sticky_position_constraint() const {
+    return inputs_.sticky_position_constraint;
+  }
+
   void SetTransform(const gfx::Transform& transform);
   const gfx::Transform& transform() const { return inputs_.transform; }
 
@@ -675,6 +681,8 @@ class CC_EXPORT Layer : public base::RefCounted<Layer> {
     bool is_container_for_fixed_position_layers : 1;
     LayerPositionConstraint position_constraint;
 
+    LayerStickyPositionConstraint sticky_position_constraint;
+
     ElementId element_id;
 
     uint32_t mutable_properties;