[turbofan] Make sure value numbering only narrows types.

src/compiler/value-numbering-reducer.h

 // Copyright 2014 the V8 project 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 V8_COMPILER_VALUE_NUMBERING_REDUCER_H_
 #define V8_COMPILER_VALUE_NUMBERING_REDUCER_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class ValueNumberingReducer final : public Reducer {
  public:
-  explicit ValueNumberingReducer(Zone* zone);
+  explicit ValueNumberingReducer(Zone* temp_zone, Zone* graph_zone);
   ~ValueNumberingReducer();
 
   Reduction Reduce(Node* node) override;
 
  private:
   enum { kInitialCapacity = 256u, kCapacityToSizeRatio = 2u };
 
   void Grow();
-  Zone* zone() const { return zone_; }
+  Zone* temp_zone() const { return temp_zone_; }
+  Zone* graph_zone() const { return graph_zone_; }
 
   Node** entries_;
   size_t capacity_;
   size_t size_;
-  Zone* zone_;
+  Zone* temp_zone_;
+  Zone* graph_zone_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_VALUE_NUMBERING_REDUCER_H_