Compute and include the offset of the sticky box to its enclosing composited layer.

cc/proto/layer_sticky_position_constraint.proto

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 syntax = "proto2";
 
+import "point.proto";
 import "rect.proto";
 import "transform.proto";
 
 option optimize_for = LITE_RUNTIME;
 
 package cc.proto;
 
 message LayerStickyPositionConstraint {
   optional bool is_sticky = 1;
   optional bool is_anchored_left = 2;
   optional bool is_anchored_right = 3;
   optional bool is_anchored_top = 4;
   optional bool is_anchored_bottom = 5;
 
   optional float left_offset = 6;
   optional float right_offset = 7;
   optional float top_offset = 8;
   optional float bottom_offset = 9;
 
+  optional Point parent_relative_sticky_box_offset = 12;
   optional Rect scroll_container_relative_sticky_box_rect = 10;
   optional Rect scroll_container_relative_containing_block_rect = 11;
 };