Fix incorrectly calculated content_size for fragments that create new FC

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.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_block_layout_algorithm.h"
 
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_fragment_builder.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_length_utils.h"
@@ skipping 86 matching lines @@
                                            border_and_padding_.InlineSum());
         current_child_ = current_child_->NextSibling();
         if (current_child_)
           return false;
       }
       state_ = kStateFinalize;
       return false;
     }
     case kStateFinalize: {
       content_size_ += border_and_padding_.block_end;
+      // Margins of the newly established formatting context do not participate
+      // in Collapsing Margins and therefore need to be added to the current
+      // content_size.
+      if (constraint_space->IsNewFormattingContext()) {
+        content_size_ += builder_->MarginStrut().BlockEndSum();

[cbiesinger, 2016/10/03 19:58:27]

That does not look right, shouldn't this be handled by the parent? We don't add
margin-start to content_size either.

[Gleb Lanbin, 2016/10/04 14:47:49]

the logic is correct, I double verified it with Ian. I moved this part to
CollapseMargins method. Hope it looks better now.

+        builder_->ClearMarginStrut();
+      }
+
       // Recompute the block-axis size now that we know our content size.
       LayoutUnit block_size = computeBlockSizeForFragment(
           *constraint_space, *style_, content_size_);
 
       builder_->SetBlockSize(block_size)
           .SetInlineOverflow(max_inline_size_)
           .SetBlockOverflow(content_size_);
       *out = builder_->ToFragment();
       state_ = kStateInit;
       return true;
@@ skipping 59 matching lines @@
 
 void NGBlockLayoutAlgorithm::UpdateMarginStrut(const NGMarginStrut& from) {
   if (!is_fragment_margin_strut_block_start_updated_) {
     builder_->SetMarginStrutBlockStart(from);
     is_fragment_margin_strut_block_start_updated_ = true;
   }
   builder_->SetMarginStrutBlockEnd(from);
 }
 
 }  // namespace blink