Unify the calculation of main thread offset of sticky element

cc/layers/layer_sticky_position_constraint.cc

 // Copyright 2013 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.
 
 #include "cc/layers/layer_sticky_position_constraint.h"
 
 #include "cc/layers/layer.h"
 
 namespace cc {
 
@@ skipping 14 matching lines @@
     const LayerStickyPositionConstraint& other)
     : is_sticky(other.is_sticky),
       is_anchored_left(other.is_anchored_left),
       is_anchored_right(other.is_anchored_right),
       is_anchored_top(other.is_anchored_top),
       is_anchored_bottom(other.is_anchored_bottom),
       left_offset(other.left_offset),
       right_offset(other.right_offset),
       top_offset(other.top_offset),
       bottom_offset(other.bottom_offset),
-      parent_relative_sticky_box_offset(
-          other.parent_relative_sticky_box_offset),
       scroll_container_relative_sticky_box_rect(
           other.scroll_container_relative_sticky_box_rect),
       scroll_container_relative_containing_block_rect(
           other.scroll_container_relative_containing_block_rect),
       nearest_layer_shifting_sticky_box(
           other.nearest_layer_shifting_sticky_box),
       nearest_layer_shifting_containing_block(
           other.nearest_layer_shifting_containing_block) {}
 
 bool LayerStickyPositionConstraint::operator==(
     const LayerStickyPositionConstraint& other) const {
   if (!is_sticky && !other.is_sticky)
     return true;
   return is_sticky == other.is_sticky &&
          is_anchored_left == other.is_anchored_left &&
          is_anchored_right == other.is_anchored_right &&
          is_anchored_top == other.is_anchored_top &&
          is_anchored_bottom == other.is_anchored_bottom &&
          left_offset == other.left_offset &&
          right_offset == other.right_offset && top_offset == other.top_offset &&
          bottom_offset == other.bottom_offset &&
-         parent_relative_sticky_box_offset ==
-             other.parent_relative_sticky_box_offset &&
          scroll_container_relative_sticky_box_rect ==
              other.scroll_container_relative_sticky_box_rect &&
          scroll_container_relative_containing_block_rect ==
              other.scroll_container_relative_containing_block_rect &&
          nearest_layer_shifting_sticky_box ==
              other.nearest_layer_shifting_sticky_box &&
          nearest_layer_shifting_containing_block ==
              other.nearest_layer_shifting_containing_block;
 }
 
 bool LayerStickyPositionConstraint::operator!=(
     const LayerStickyPositionConstraint& other) const {
   return !(*this == other);
 }
 
 int LayerStickyPositionConstraint::NearestStickyAncestor() {
   return (nearest_layer_shifting_sticky_box != Layer::INVALID_ID)
              ? nearest_layer_shifting_sticky_box
              : nearest_layer_shifting_containing_block;
 }
 
 }  // namespace cc