Ignore zero-height fragments during margin collapsing

third_party/WebKit/Source/core/layout/ng/ng_fragment_builder.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_builder.h"
 
 namespace blink {
 
 NGFragmentBuilder::NGFragmentBuilder(
     NGPhysicalFragmentBase::NGFragmentType type)
     : type_(type),
       writing_mode_(HorizontalTopBottom),
       direction_(LeftToRight),
-      is_margin_strut_block_start_updated_(false),
-      is_margin_strut_block_end_updated_(false) {}
+      is_margin_strut_block_start_updated_(false) {}
 
 NGFragmentBuilder& NGFragmentBuilder::SetWritingMode(
     NGWritingMode writing_mode) {
   writing_mode_ = writing_mode;
   return *this;
 }
 
 NGFragmentBuilder& NGFragmentBuilder::SetDirection(NGDirection direction) {
   direction_ = direction;
   return *this;
@@ skipping 21 matching lines @@
 
 NGFragmentBuilder& NGFragmentBuilder::AddChild(NGFragment* child,
                                                NGLogicalOffset offset) {
   DCHECK_EQ(type_, NGPhysicalFragmentBase::FragmentBox)
       << "Only box fragments can have children";
   children_.append(child->PhysicalFragment());
   offsets_.append(offset);
   return *this;
 }
 
-NGFragmentBuilder& NGFragmentBuilder::SetMarginStrutBlockStart(
+NGFragmentBuilder& NGFragmentBuilder::UpdateMarginStrut(
     const NGMarginStrut& from) {
+  if (!is_margin_strut_block_start_updated_)
+    SetMarginStrutBlockStart(from);
+  SetMarginStrutBlockEnd(from);
+  return *this;
+}
+
+void NGFragmentBuilder::SetMarginStrutBlockStart(const NGMarginStrut& from) {
   DCHECK(!is_margin_strut_block_start_updated_);
   margin_strut_.margin_block_start = from.margin_block_start;
   margin_strut_.negative_margin_block_start = from.negative_margin_block_start;
   is_margin_strut_block_start_updated_ = true;
-  return *this;
 }
 
-NGFragmentBuilder& NGFragmentBuilder::SetMarginStrutBlockEnd(
-    const NGMarginStrut& from) {
-  DCHECK(!is_margin_strut_block_end_updated_);
+void NGFragmentBuilder::SetMarginStrutBlockEnd(const NGMarginStrut& from) {
   margin_strut_.margin_block_end = from.margin_block_end;
   margin_strut_.negative_margin_block_end = from.negative_margin_block_end;
-  is_margin_strut_block_end_updated_ = true;
-  return *this;
 }
 
 NGPhysicalFragment* NGFragmentBuilder::ToFragment() {
   // TODO(layout-ng): Support text fragments
   DCHECK_EQ(type_, NGPhysicalFragmentBase::FragmentBox);
   DCHECK_EQ(offsets_.size(), children_.size());
 
   NGPhysicalSize physical_size = size_.ConvertToPhysical(writing_mode_);
   HeapVector<Member<const NGPhysicalFragmentBase>> children;
   children.reserveCapacity(children_.size());
 
   for (size_t i = 0; i < children_.size(); ++i) {
     NGPhysicalFragmentBase* child = children_[i].get();
     child->SetOffset(offsets_[i].ConvertToPhysical(
         writing_mode_, direction_, physical_size, child->Size()));
     children.append(child);
   }
   return new NGPhysicalFragment(physical_size,
                                 overflow_.ConvertToPhysical(writing_mode_),
                                 children, margin_strut_);
 }
 
 }  // namespace blink