[LayoutNG] Fix orthogonal writing mode child margin strut from being used in collapsing margins cal…

third_party/WebKit/Source/core/layout/ng/ng_fragment.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_fragment.h"
 
-namespace blink {}  // namespace blink
+#include "core/layout/ng/ng_physical_fragment.h"
+
+namespace blink {
+
+NGMarginStrut NGFragment::MarginStrut() const {
+  // NOTE: Accessing the margin strut ignoring the writing mode here is fine.
+  // Changing the writing mode establishes a new formatting context, for which
+  // a margin strut is never set for a fragment.
+  return toNGPhysicalFragment(physical_fragment_)->MarginStrut();
+}
+
+}  // namespace blink