[turbofan] Introduce PretenureFlagOf helper function.

src/compiler/simplified-operator.cc

Index: src/compiler/simplified-operator.cc
diff --git a/src/compiler/simplified-operator.cc b/src/compiler/simplified-operator.cc
index 86096fa5c742d9120b4d54a952e94429e8dac0ce..40102fa8526db4cade7f9797a173c14171103a64 100644
--- a/src/compiler/simplified-operator.cc
+++ b/src/compiler/simplified-operator.cc
@@ -332,6 +332,11 @@ NumberOperationHint NumberOperationHintOf(const Operator* op) {
   return OpParameter<NumberOperationHint>(op);
 }
 
+PretenureFlag PretenureFlagOf(const Operator* op) {
+  DCHECK_EQ(IrOpcode::kAllocate, op->opcode());
+  return OpParameter<PretenureFlag>(op);
+}
+
 #define PURE_OP_LIST(V)                                          \
   V(BooleanNot, Operator::kNoProperties, 1, 0)                   \
   V(NumberEqual, Operator::kCommutative, 2, 0)                   \