[LayoutNG] Initial NGLayoutOpportunityIterator implementation

Add initial simple NGLayoutOpportunityIterator implementation. Does not
yet handle exclusions, inlines or bfcs.

R=ikilpatrick@chromium.org,cbiesinger@chromium.org
BUG=635619

Review-Url: https://codereview.chromium.org/2286403004
Cr-Commit-Position: refs/heads/master@{#415417}

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

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

@@ -112,7 +112,7 @@ class CORE_EXPORT NGLayoutOpportunityIterator final {
         for_inline_or_bfc_(for_inline_or_bfc) {}
   ~NGLayoutOpportunityIterator() {}
 
-  const NGDerivedConstraintSpace* Next();
+  NGConstraintSpace* Next();
 
  private:
   Persistent<NGConstraintSpace> constraint_space_;

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

@@ -40,6 +40,21 @@ TEST(NGConstraintSpaceTest, WritingMode) {
   EXPECT_EQ(FragmentNone, vert_space->BlockFragmentationType());
 }
 
+TEST(NGConstraintSpaceTest, LayoutOpportunities) {
+  NGPhysicalSize physical_size;
+  physical_size.width = LayoutUnit(600);
+  physical_size.height = LayoutUnit(400);
+  auto* physical_space = new NGPhysicalConstraintSpace(physical_size);
+  auto* space = new NGConstraintSpace(HorizontalTopBottom, physical_space);
+
+  bool for_inline_or_bfc = false;
+  auto iterator = space->LayoutOpportunities(NGClearNone, for_inline_or_bfc);
+
+  auto firstOpportunity = iterator.Next();
+  EXPECT_EQ(LayoutUnit(600), firstOpportunity->Size().inline_size);
+  EXPECT_EQ(LayoutUnit(400), firstOpportunity->Size().block_size);
+}
+
 }  // namespace
 
 }  // namespace blink

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

@@ -45,11 +45,11 @@ void NGPhysicalConstraintSpace::AddExclusion(const NGExclusion,
   // TODO(layout-ng): Implement.
 }
 
-DoublyLinkedList<const NGExclusion> NGPhysicalConstraintSpace::Exclusions(
-    unsigned options) const {
-  DoublyLinkedList<const NGExclusion> exclusions;
-  // TODO(layout-ng): Implement.
-  return exclusions;
+const DoublyLinkedList<const NGExclusion>*
+NGPhysicalConstraintSpace::Exclusions(unsigned options) const {
+  // TODO(layout-ng): Filter based on options? Perhaps layout Opportunities
+  // should filter instead?
+  return &exclusions_;
 }
 
 }  // namespace blink

third_party/WebKit/Source/core/layout/ng/ng_physical_constraint_space.h

@@ -47,7 +47,8 @@ class CORE_EXPORT NGPhysicalConstraintSpace final
   NGPhysicalSize ContainerSize() const { return container_size_; }
 
   void AddExclusion(const NGExclusion, unsigned options = 0);
-  DoublyLinkedList<const NGExclusion> Exclusions(unsigned options = 0) const;
+  const DoublyLinkedList<const NGExclusion>* Exclusions(
+      unsigned options = 0) const;
 
   DEFINE_INLINE_TRACE() {}