[turbofan] Make sure value numbering only narrows types.

test/unittests/compiler/value-numbering-reducer-unittest.cc

 // 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.
 
 #include <limits>
 
 #include "src/compiler/graph.h"
 #include "src/compiler/node.h"
 #include "src/compiler/operator.h"
 #include "src/compiler/value-numbering-reducer.h"
@@ skipping 10 matching lines @@
                  0) {}
 };
 
 
 static const TestOperator kOp0(0, Operator::kIdempotent, 0, 1);
 static const TestOperator kOp1(1, Operator::kIdempotent, 1, 1);
 
 
 class ValueNumberingReducerTest : public TestWithZone {
  public:
-  ValueNumberingReducerTest() : graph_(zone()), reducer_(zone()) {}
+  ValueNumberingReducerTest()
+      : graph_(zone()), reducer_(zone(), graph()->zone()) {}
 
  protected:
   Reduction Reduce(Node* node) { return reducer_.Reduce(node); }
 
   Graph* graph() { return &graph_; }
 
  private:
   Graph graph_;
   ValueNumberingReducer reducer_;
 };
@@ skipping 79 matching lines @@
 
 TEST_F(ValueNumberingReducerTest, WontReplaceNodeWithItself) {
   Node* n = graph()->NewNode(&kOp0);
   EXPECT_FALSE(Reduce(n).Changed());
   EXPECT_FALSE(Reduce(n).Changed());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8