Collapse margins before child that uses legacy layout.

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/inline/ng_inline_node.h"
 #include "core/layout/ng/ng_absolute_utils.h"
 #include "core/layout/ng/ng_block_child_iterator.h"
 #include "core/layout/ng/ng_constraint_space.h"
@@ skipping 326 matching lines @@
   // strut as they do not participate in margin collapsing.
   if (is_inflow) {
     child_bfc_offset.inline_offset += curr_child_margins_.inline_start;
     // Append the current margin strut with child's block start margin.
     // Non empty border/padding, and new FC use cases are handled inside of the
     // child's layout.
     if (!IsNewFormattingContextForBlockLevelChild(Style(), *child))
       curr_margin_strut_.Append(curr_child_margins_.block_start);
   }
 
-  // Should collapse margins if inline.
-  if (child->IsInline()) {
+  // TODO(glebl): Handle the case when a legacy block has border/padding.

[ikilpatrick, 2017/04/24 20:27:50]

This should be fine right? As these should always be new FCs?

[Gleb Lanbin, 2017/04/24 21:15:33]

yes, on a second thought, I think this TODO is not needed here.

+  bool is_legacy_block =
+      child->IsBlock() && !ToNGBlockNode(child)->CanUseNewLayout();
+
+  // Should collapse margins if inline or legacy block
+  if (child->IsInline() || is_legacy_block) {
     curr_bfc_offset_.block_offset += curr_margin_strut_.Sum();
     MaybeUpdateFragmentBfcOffset(ConstraintSpace(), curr_bfc_offset_,
                                  &container_builder_);
     PositionPendingFloats(curr_bfc_offset_.block_offset, &container_builder_,
                           MutableConstraintSpace());
     curr_margin_strut_ = {};
   }
   child_bfc_offset.block_offset = curr_bfc_offset_.block_offset;
   return child_bfc_offset;
 }
@@ skipping 223 matching lines @@
     if (is_new_bfc) {
       space_available -= child_bfc_offset.block_offset;
     }
   }
   space_builder_.SetFragmentainerSpaceAvailable(space_available);
 
   return space_builder_.ToConstraintSpace(
       FromPlatformWritingMode(child_style.GetWritingMode()));
 }
 }  // namespace blink