[turbofan] Restore basic write barrier elimination.

src/compiler/machine-operator.h

 // Copyright 2013 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_MACHINE_OPERATOR_H_
 #define V8_COMPILER_MACHINE_OPERATOR_H_
 
 #include "src/base/flags.h"
 #include "src/machine-type.h"
 
@@ skipping 14 matching lines @@
   bool IsSupported() const { return op_ != nullptr; }
   const Operator* op() const {
     DCHECK_NOT_NULL(op_);
     return op_;
   }
 
  private:
   const Operator* const op_;
 };
 
-// Supported write barrier modes.
-enum WriteBarrierKind {
-  kNoWriteBarrier,
-  kMapWriteBarrier,
-  kPointerWriteBarrier,
-  kFullWriteBarrier
-};
-
-std::ostream& operator<<(std::ostream& os, WriteBarrierKind);
-
 
 // A Load needs a MachineType.
 typedef MachineType LoadRepresentation;
 
 LoadRepresentation LoadRepresentationOf(Operator const*);
 
 // A Store needs a MachineType and a WriteBarrierKind in order to emit the
 // correct write barrier.
 class StoreRepresentation final {
  public:
@@ skipping 501 matching lines @@
 };
 
 
 DEFINE_OPERATORS_FOR_FLAGS(MachineOperatorBuilder::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_H_