[layoutng] Make the layout algorithm actually compute and store positions and sizes

third_party/WebKit/Source/core/layout/ng/ng_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 NGFragment_h
 #define NGFragment_h
 
 #include "core/CoreExport.h"
 #include "core/layout/ng/ng_fragment_base.h"
 #include "platform/LayoutUnit.h"
@@ skipping 10 matching lines @@
              LayoutUnit blockOverflow)
       : NGFragmentBase(inlineSize, blockSize, inlineOverflow, blockOverflow) {
     m_isText = false;
   }
 
   DEFINE_INLINE_TRACE_AFTER_DISPATCH() {
     visitor->trace(m_children);
     NGFragmentBase::traceAfterDispatch(visitor);
   }
 
+  void swapChildren(HeapVector<Member<const NGFragmentBase>>& children) {
+    m_children.swap(children);
+  }
+
  private:
   HeapVector<Member<const NGFragmentBase>> m_children;
   bool m_isText;
 };
 
 }  // namespace blink
 
 #endif  // NGFragment_h