Combine 2 exclusions in Layout Opportunity Tree if they shadow each other

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

 // 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.
 
 #ifndef NGLayoutOpportunityTreeNode_h
 #define NGLayoutOpportunityTreeNode_h
 
 #include "core/layout/ng/geometry/ng_edge.h"
 #include "core/layout/ng/geometry/ng_logical_rect.h"
 #include "core/layout/ng/ng_exclusion.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 // 3 node R-Tree that represents available space(left, bottom, right) or
 // layout opportunity after the parent spatial rectangle is split by the
 // exclusion rectangle.
 struct CORE_EXPORT NGLayoutOpportunityTreeNode
-    : public GarbageCollected<NGLayoutOpportunityTreeNode> {
+    : public GarbageCollectedFinalized<NGLayoutOpportunityTreeNode> {
  public:
   // Default constructor.
   // Creates a Layout Opportunity tree node that is limited by it's own edge
   // from above.
   // @param opportunity The layout opportunity for this node.
   NGLayoutOpportunityTreeNode(const NGLogicalRect opportunity);
 
   // Constructor that creates a node with explicitly set exclusion edge.
   // @param opportunity The layout opportunity for this node.
   // @param exclusion_edge Edge that limits this node's opportunity from above.
   NGLayoutOpportunityTreeNode(const NGLogicalRect opportunity,
                               NGEdge exclusion_edge);
 
   // Children of the node.
   Member<NGLayoutOpportunityTreeNode> left;
   Member<NGLayoutOpportunityTreeNode> bottom;
   Member<NGLayoutOpportunityTreeNode> right;
 
   // The top layout opportunity associated with this node.
   NGLogicalRect opportunity;
 
   // Edge that limits this layout opportunity from above.
   NGEdge exclusion_edge;
 
-  // Exclusion that splits apart this layout opportunity.
-  const NGExclusion* exclusion;  // Not owned.
+  // Exclusions that splits apart this layout opportunity.
+  Vector<const NGExclusion*> exclusions;  // Not owned.
+
+  // Exclusion that represent all combined exclusions that
+  // split this node.
+  std::unique_ptr<NGExclusion> combined_exclusion;
 
   // Whether this node is a leaf node.
-  // The node is a leaf if it doesn't have an exclusion that splits it apart.
-  bool IsLeafNode() const { return !exclusion; }
+  // The node is a leaf if it doesn't have exclusions that split it apart.
+  bool IsLeafNode() const { return exclusions.isEmpty(); }
 
   String ToString() const;
 
   DECLARE_TRACE();
 };
 
 inline std::ostream& operator<<(std::ostream& stream,
                                 const NGLayoutOpportunityTreeNode& value) {
   return stream << value.ToString();
 }
 
 inline std::ostream& operator<<(std::ostream& out,
                                 const NGLayoutOpportunityTreeNode* value) {
   return out << (value ? value->ToString() : "(null)");
 }
 
 }  // namespace blink
 #endif  // NGLayoutOpportunityTreeNode_h