[turbofan] Slightly improve typing rule for NumberAdd.

src/compiler/operation-typer.h

 // Copyright 2016 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_OPERATION_TYPER_H_
 #define V8_COMPILER_OPERATION_TYPER_H_
 
 #include "src/base/flags.h"
 #include "src/compiler/opcodes.h"
 
@@ skipping 57 matching lines @@
   Type* AddRanger(double lhs_min, double lhs_max, double rhs_min,
                   double rhs_max);
   Type* SubtractRanger(RangeType* lhs, RangeType* rhs);
   Type* MultiplyRanger(Type* lhs, Type* rhs);
 
   Zone* zone() const { return zone_; }
 
   Zone* const zone_;
   TypeCache const& cache_;
 
+  Type* infinity_;
+  Type* minus_infinity_;
   Type* singleton_false_;
   Type* singleton_true_;
   Type* singleton_the_hole_;
   Type* signed32ish_;
   Type* unsigned32ish_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPERATION_TYPER_H_