[turbofan] Eliminate redundant masking operations for word8/word16 stores.

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 9774f63cfe50ea1345d315315d51d081828c56bd..58be985d32880724f27e9b7adc0f6faf48e7b51d 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -49,6 +49,8 @@ size_t hash_value(StoreRepresentation);
 
 std::ostream& operator<<(std::ostream&, StoreRepresentation);
 
+StoreRepresentation const& StoreRepresentationOf(Operator const*);
+
 
 // Interface for building machine-level operators. These operators are
 // machine-level but machine-independent and thus define a language suitable