Collapse margins before child that uses legacy layout.

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

Index: third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
index e4f148ad47b744dc0ff123f04fbb55dd2f2b188d..0d4e4ab9d64f7098d9dbc2d06e7bdda32daff2e7 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.cc
@@ -344,8 +344,12 @@ NGLogicalOffset NGBlockLayoutAlgorithm::PrepareChildLayout(
       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_);