Do not collapse margins with padding/border b/w parent and first/last child

third_party/WebKit/Source/core/layout/ng/ng_units.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_units.h"
 
 #include "core/layout/ng/ng_writing_mode.h"
 
 namespace blink {
 
@@ skipping 61 matching lines @@
 
 void NGMarginStrut::AppendMarginBlockEnd(const LayoutUnit& value) {
   if (value < 0) {
     negative_margin_block_end =
         -std::max(value.abs(), negative_margin_block_end.abs());
   } else {
     margin_block_end = std::max(value, margin_block_end);
   }
 }
 
+void NGMarginStrut::SetMarginBlockStart(const LayoutUnit& value) {
+  if (value < 0) {
+    negative_margin_block_start = value;
+  } else {
+    margin_block_start = value;
+  }
+}
+
 void NGMarginStrut::SetMarginBlockEnd(const LayoutUnit& value) {
   if (value < 0) {
     negative_margin_block_end = value;
   } else {
     margin_block_end = value;
   }
 }
 
 String NGMarginStrut::ToString() const {
   return String::format(
       "Start: (%d %d) End: (%d %d)", negative_margin_block_start.toInt(),
       margin_block_start.toInt(), negative_margin_block_end.toInt(),
       margin_block_end.toInt());
 }
 
 bool NGMarginStrut::operator==(const NGMarginStrut& other) const {
   return std::tie(other.margin_block_start, other.margin_block_end,
                   other.negative_margin_block_start,
                   other.negative_margin_block_end) ==
          std::tie(margin_block_start, margin_block_end,
                   negative_margin_block_start, negative_margin_block_end);
 }
 
 }  // namespace blink