blink: Cleanup core class forward declarations

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/ng_units.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
-class NGConstraintSpace;
 struct NGExclusion;
 
 // 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> {
   // Default constructor.
   // Creates a Layout Opportunity tree node that is limited by it's own edge
   // from above.
@@ skipping 22 matching lines @@
 
   // 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; }
 
   DECLARE_TRACE();
 };
 
 }  // namespace blink
 #endif  // NGLayoutOpportunityTreeNode_h