Revert of [turbofan] Restore basic write barrier elimination.

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 99d1b955c197566d9c3876b064fb34fe72029810..faa3a5d4b47378788b54269bc731d52a23454c42 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -31,6 +31,16 @@
  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.