[LayoutNG] Initial NGLayoutOpportunityIterator implementation

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

Index: third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
index fe00b9a702e875f4a9318cbfad5a38faf161c795..79dfe7ea91f743e459c61635b72f3a3a67a27dca 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_constraint_space.cc
@@ -81,7 +81,6 @@ void NGConstraintSpace::Subtract(const NGFragment*) {
 NGLayoutOpportunityIterator NGConstraintSpace::LayoutOpportunities(
     unsigned clear,
     bool for_inline_or_bfc) {
-  // TODO(layout-ng): Implement.
   NGLayoutOpportunityIterator iterator(this, clear, for_inline_or_bfc);
   return iterator;
 }
@@ -131,4 +130,12 @@ void NGConstraintSpace::SetFragmentationType(NGFragmentationType 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