[turbofan] Avoid unnecessary write barriers and improve code generation.

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 14ad9e03d11e74722230e080458d6e0673c3aa06..5240317b3af1bed33ad9cc649dc697774dfbbd91 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -49,7 +49,12 @@ TruncationMode TruncationModeOf(Operator const*);
 
 
 // Supported write barrier modes.
-enum WriteBarrierKind { kNoWriteBarrier, kFullWriteBarrier };
+enum WriteBarrierKind {
+  kNoWriteBarrier,
+  kMapWriteBarrier,
+  kPointerWriteBarrier,
+  kFullWriteBarrier
+};
 
 std::ostream& operator<<(std::ostream& os, WriteBarrierKind);