[turbofan] Introduce PretenureFlagOf helper function.

src/compiler/simplified-operator.h

Index: src/compiler/simplified-operator.h
diff --git a/src/compiler/simplified-operator.h b/src/compiler/simplified-operator.h
index 611c31d23b716b1b37ced9960c4258b13b0a067b..d59faa985f679f3cc642df06c69c827cc445c0f7 100644
--- a/src/compiler/simplified-operator.h
+++ b/src/compiler/simplified-operator.h
@@ -183,6 +183,8 @@ std::ostream& operator<<(std::ostream&, NumberOperationHint);
 NumberOperationHint NumberOperationHintOf(const Operator* op)
     WARN_UNUSED_RESULT;
 
+PretenureFlag PretenureFlagOf(const Operator* op) WARN_UNUSED_RESULT;
+
 // Interface for building simplified operators, which represent the
 // medium-level operations of V8, including adding numbers, allocating objects,
 // indexing into objects and arrays, etc.