[LayoutNG] Initial support for multicol, introducing NGBlockBreakToken.

third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.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 NGPhysicalBoxFragment_h
 #define NGPhysicalBoxFragment_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_physical_fragment.h"
 #include "core/layout/ng/ng_units.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class NGBlockNode;
 
 class CORE_EXPORT NGPhysicalBoxFragment final : public NGPhysicalFragment {
  public:
   // This modifies the passed-in children vector.
   NGPhysicalBoxFragment(
       NGPhysicalSize size,
       NGPhysicalSize overflow,
       HeapVector<Member<const NGPhysicalFragment>>& children,
       HeapLinkedHashSet<WeakMember<NGBlockNode>>& out_of_flow_descendants,
       Vector<NGStaticPosition>& out_of_flow_positions,
-      NGMarginStrut margin_strut);
+      NGMarginStrut margin_strut,
+      NGBreakToken* break_token = nullptr);
 
   const HeapVector<Member<const NGPhysicalFragment>>& Children() const {
     return children_;
   }
 
   NGMarginStrut MarginStrut() const { return margin_strut_; }
 
   DECLARE_TRACE_AFTER_DISPATCH();
 
  private:
   HeapVector<Member<const NGPhysicalFragment>> children_;
   NGMarginStrut margin_strut_;
 };
 
 WILL_NOT_BE_EAGERLY_TRACED_CLASS(NGPhysicalBoxFragment);
 
 DEFINE_TYPE_CASTS(NGPhysicalBoxFragment,
                   NGPhysicalFragment,
                   fragment,
                   fragment->Type() == NGPhysicalFragment::kFragmentBox,
                   fragment.Type() == NGPhysicalFragment::kFragmentBox);
 
 }  // namespace blink
 
 #endif  // NGPhysicalBoxFragment_h