Add support of leader_point in NGLayoutOpportunityIterator.

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

Index: third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc
index 5eb1a7c78a601292445a6b44c4be74221492257c..cdbc00325fa0b76f7ada8346b374d4ccd9da3f24 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc
@@ -150,6 +150,10 @@ NGLayoutOpportunity GetTopSpace(const NGLayoutOpportunity& parent_opportunity,
 void InsertExclusion(NGLayoutOpportunityTreeNode* node,
                      const NGLogicalRect* exclusion,
                      NGLayoutOpportunities& opportunities) {
+  // Base case: size of the exclusion is empty.
+  if (exclusion->size.IsEmpty())
+    return;
+
   // Base case: there is no node.
   if (!node)
     return;
@@ -210,13 +214,39 @@ bool CompareNGLayoutOpportunitesByStartPoint(const NGLayoutOpportunity& lhs,
   return rhs.size.inline_size < lhs.size.inline_size;
 }
 
+void RunPreconditionChecks(const NGConstraintSpace& space,
+                           const NGLogicalOffset& origin_point,
+                           const NGLogicalOffset& leader_point) {
+  DCHECK_GE(origin_point, space.Offset())
+      << "Origin point" << origin_point
+      << " should lay below the constraint space's offset " << space.Offset();
+
+  DCHECK_GE(leader_point, space.Offset())
+      << "Leader point" << leader_point
+      << " should lay below the constraint space's offset " << space.Offset();
+}
+
+NGLogicalRect ToLeaderExclusion(const NGLogicalOffset& origin_point,
+                                const NGLogicalOffset& leader_point) {
+  NGLogicalRect leader_exclusion;
+  leader_exclusion.offset.inline_offset = origin_point.inline_offset;
+  leader_exclusion.offset.block_offset = origin_point.block_offset;
+  leader_exclusion.size.inline_size =
+      leader_point.inline_offset - origin_point.inline_offset;
+  leader_exclusion.size.block_size =
+      leader_point.block_offset - origin_point.block_offset;
+  return leader_exclusion;
+}
+
 }  // namespace
 
 NGLayoutOpportunityIterator::NGLayoutOpportunityIterator(
     NGConstraintSpace* space,
-    const NGLogicalOffset origin_point,
-    const NGLogicalOffset leader_point)
-    : constraint_space_(space), leader_point_(leader_point) {
+    const NGLogicalOffset& origin_point,
+    const NGLogicalOffset& leader_point)
+    : constraint_space_(space) {
+  RunPreconditionChecks(*space, origin_point, leader_point);
+
   // TODO(chrome-layout-team): Combine exclusions that shadow each other.
   auto& exclusions = constraint_space_->PhysicalSpace()->Exclusions();
   DCHECK(std::is_sorted(exclusions.begin(), exclusions.end(),
@@ -227,6 +257,11 @@ NGLayoutOpportunityIterator::NGLayoutOpportunityIterator(
       CreateLayoutOpportunityFromConstraintSpace(*space, origin_point);
   opportunity_tree_root_ = new NGLayoutOpportunityTreeNode(initial_opportunity);
 
+  const NGLogicalRect leader_exclusion =
+      ToLeaderExclusion(origin_point, leader_point);
+  InsertExclusion(MutableOpportunityTreeRoot(), &leader_exclusion,
+                  opportunities_);
+
   for (const auto& exclusion : exclusions) {
     InsertExclusion(MutableOpportunityTreeRoot(), exclusion.get(),
                     opportunities_);