Fragment that establishes new BFC knows it's BFC offset in parent space

third_party/WebKit/Source/core/layout/ng/ng_constraint_space_builder.cc

 // Copyright 2016 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 "core/layout/ng/ng_constraint_space_builder.h"
 
 #include "core/layout/ng/ng_length_utils.h"
 
 namespace blink {
 
@@ skipping 99 matching lines @@
   return *this;
 }
 
 NGConstraintSpaceBuilder& NGConstraintSpaceBuilder::SetWritingMode(
     NGWritingMode writing_mode) {
   writing_mode_ = writing_mode;
   return *this;
 }
 
 NGConstraintSpace* NGConstraintSpaceBuilder::ToConstraintSpace() {
+  // Exclusions do not pass the formatting context boundary.
+  std::shared_ptr<NGExclusions> exclusions(
+      is_new_fc_ ? std::make_shared<NGExclusions>() : exclusions_);
+
   // Whether the child and the containing block are parallel to each other.
   // Example: vertical-rl and vertical-lr
   bool is_in_parallel_flow = (parent_writing_mode_ == kHorizontalTopBottom) ==
                              (writing_mode_ == kHorizontalTopBottom);
 
+  NGLogicalOffset bfc_offset = is_new_fc_ ? NGLogicalOffset() : bfc_offset_;
+  NGMarginStrut margin_strut = is_new_fc_ ? NGMarginStrut() : margin_strut_;
+
   if (is_in_parallel_flow) {
     return new NGConstraintSpace(
         static_cast<NGWritingMode>(writing_mode_),
         static_cast<TextDirection>(text_direction_),
         {available_size_.inline_size, available_size_.block_size},
         {percentage_resolution_size_.inline_size,
          percentage_resolution_size_.block_size},
         fragmentainer_space_available_, is_fixed_size_inline_,
         is_fixed_size_block_, is_shrink_to_fit_,
         is_inline_direction_triggers_scrollbar_,
         is_block_direction_triggers_scrollbar_,
         static_cast<NGFragmentationType>(fragmentation_type_), is_new_fc_,
-        margin_strut_, bfc_offset_, exclusions_);
+        margin_strut, bfc_offset, exclusions);
   }
 
   return new NGConstraintSpace(
       static_cast<NGWritingMode>(writing_mode_),
       static_cast<TextDirection>(text_direction_),
       {available_size_.block_size, available_size_.inline_size},
       {percentage_resolution_size_.block_size,
        percentage_resolution_size_.inline_size},
       fragmentainer_space_available_, is_fixed_size_block_,
       is_fixed_size_inline_, is_shrink_to_fit_,
       is_block_direction_triggers_scrollbar_,
       is_inline_direction_triggers_scrollbar_,
       static_cast<NGFragmentationType>(fragmentation_type_), is_new_fc_,
-      margin_strut_, bfc_offset_, exclusions_);
+      margin_strut, bfc_offset, exclusions);
 }
 
 }  // namespace blink