[LayoutNG] Convert physical fragments to being RefCounted.

third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc

Index: third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc
diff --git a/third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc b/third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc
index 845b55fb7429b0b769db1241155bd6b2b53be948..ad9d2fcd235cea46b55a38c9c898c6987e8b5677 100644
--- a/third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc
+++ b/third_party/WebKit/Source/core/layout/ng/ng_physical_box_fragment.cc
@@ -10,11 +10,12 @@ NGPhysicalBoxFragment::NGPhysicalBoxFragment(
     LayoutObject* layout_object,
     NGPhysicalSize size,
     NGPhysicalSize overflow,
-    HeapVector<Member<NGPhysicalFragment>>& children,
-    HeapLinkedHashSet<WeakMember<NGBlockNode>>& out_of_flow_descendants,
+    Vector<RefPtr<NGPhysicalFragment>>& children,
+    PersistentHeapLinkedHashSet<WeakMember<NGBlockNode>>&
+        out_of_flow_descendants,
     Vector<NGStaticPosition>& out_of_flow_positions,
-    HeapVector<Member<NGFloatingObject>>& unpositioned_floats,
-    HeapVector<Member<NGFloatingObject>>& positioned_floats,
+    Vector<Persistent<NGFloatingObject>>& unpositioned_floats,
+    Vector<Persistent<NGFloatingObject>>& positioned_floats,
     const WTF::Optional<NGLogicalOffset>& bfc_offset,
     const NGMarginStrut& end_margin_strut,
     NGBreakToken* break_token)
@@ -32,9 +33,4 @@ NGPhysicalBoxFragment::NGPhysicalBoxFragment(
   children_.swap(children);
 }
 
-DEFINE_TRACE_AFTER_DISPATCH(NGPhysicalBoxFragment) {
-  visitor->trace(children_);
-  NGPhysicalFragment::traceAfterDispatch(visitor);
-}
-
 }  // namespace blink