Change NGLayoutOpportunityIterator constructor to work with const CS.

third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.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 NGLayoutOpportunityIterator_h
 #define NGLayoutOpportunityIterator_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_layout_opportunity_tree_node.h"
@@ skipping 15 matching lines @@
   //
   // @param space Constraint space with exclusions for which this iterator needs
   //              to generate layout opportunities.
   // @param opt_origin_point Optional origin_point parameter that is used as a
   //                         default start point for layout opportunities.
   // @param opt_leader_point Optional 'leader' parameter that is used to specify
   //                         the ending point of temporary excluded rectangle
   //                         which starts from 'origin'. This rectangle may
   //                         represent a text fragment for example.
   NGLayoutOpportunityIterator(
-      NGConstraintSpace* space,
+      const NGConstraintSpace* space,
       const WTF::Optional<NGLogicalOffset>& opt_origin_point = WTF::nullopt,
       const WTF::Optional<NGLogicalOffset>& opt_leader_point = WTF::nullopt);
 
   // Gets the next Layout Opportunity or nullptr if the search is exhausted.
   // TODO(chrome-layout-team): Refactor with using C++ <iterator> library.
   const NGLayoutOpportunity Next();
 
  private:
   // Mutable Getters.
   NGLayoutOpportunityTreeNode* MutableOpportunityTreeRoot() {
     return opportunity_tree_root_.get();
   }
 
   // Read-only Getters.
   const NGLayoutOpportunityTreeNode* OpportunityTreeRoot() const {
     return opportunity_tree_root_.get();
   }
 
-  NGConstraintSpace* constraint_space_;
+  const NGConstraintSpace* constraint_space_;
 
   NGLayoutOpportunities opportunities_;
   NGLayoutOpportunities::const_iterator opportunity_iter_;
   Persistent<NGLayoutOpportunityTreeNode> opportunity_tree_root_;
 };
 
 }  // namespace blink
 
 #endif  // NGLayoutOpportunityIterator_h