[turbofan] Add the StackSlot operator to turbofan.

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 196760cb9ef6c2ecc08dcf92dabb123c0fb76821..dfbad85ec8b38959ffc16f6cf0f911b6cb48ac63 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -102,6 +102,7 @@ typedef MachineRepresentation CheckedStoreRepresentation;
 
 CheckedStoreRepresentation CheckedStoreRepresentationOf(Operator const*);
 
+MachineRepresentation StackSlotRepresentationOf(Operator const* op);
 
 // Interface for building machine-level operators. These operators are
 // machine-level but machine-independent and thus define a language suitable
@@ -305,6 +306,8 @@ class MachineOperatorBuilder final : public ZoneObject {
   // store [base + index], value
   const Operator* Store(StoreRepresentation rep);
 
+  const Operator* StackSlot(MachineRepresentation rep);
+
   // Access to the machine stack.
   const Operator* LoadStackPointer();
   const Operator* LoadFramePointer();