[LayoutNG] Initial NGLayoutOpportunityIterator implementation

third_party/WebKit/Source/core/layout/ng/ng_constraint_space.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_constraint_space.h"
 
 #include "core/layout/ng/ng_units.h"
 
 namespace blink {
 
@@ skipping 63 matching lines @@
           : physical_space_->width_direction_fragmentation_type_);
 }
 
 void NGConstraintSpace::Subtract(const NGFragment*) {
   // TODO(layout-ng): Implement.
 }
 
 NGLayoutOpportunityIterator NGConstraintSpace::LayoutOpportunities(
     unsigned clear,
     bool for_inline_or_bfc) {
-  // TODO(layout-ng): Implement.
   NGLayoutOpportunityIterator iterator(this, clear, for_inline_or_bfc);
   return iterator;
 }
 
 void NGConstraintSpace::SetContainerSize(NGLogicalSize container_size) {
   if (writing_mode_ == HorizontalTopBottom) {
     physical_space_->container_size_.width = container_size.inline_size;
     physical_space_->container_size_.height = container_size.block_size;
   } else {
     physical_space_->container_size_.width = container_size.block_size;
@@ skipping 29 matching lines @@
               FragmentNone);
     physical_space_->height_direction_fragmentation_type_ = type;
   } else {
     DCHECK_EQ(static_cast<NGFragmentationType>(
                   physical_space_->height_direction_fragmentation_type_),
               FragmentNone);
     physical_space_->width_direction_triggers_scrollbar_ = type;
   }
 }
 
+NGConstraintSpace* NGLayoutOpportunityIterator::Next() {
+  auto* exclusions = constraint_space_->PhysicalSpace()->Exclusions();
+  if (!exclusions->head())
+    return new NGConstraintSpace(constraint_space_->WritingMode(),
+                                 constraint_space_->PhysicalSpace());
+  return nullptr;
+}
+
 }  // namespace blink