[Interpreter] Add support for loading from / storing to outer context variables.

test/cctest/compiler/c-signature.h

Index: test/cctest/compiler/c-signature.h
diff --git a/test/cctest/compiler/c-signature.h b/test/cctest/compiler/c-signature.h
index 6a17a29856b421254b18ae1c416ad72ff45849c7..bc0345708e3767ff0f9cb34156e78129d00f85fb 100644
--- a/test/cctest/compiler/c-signature.h
+++ b/test/cctest/compiler/c-signature.h
@@ -36,6 +36,12 @@ inline MachineType MachineTypeForC() {
   return kMachAnyTagged;
 }
 
+template <typename T>
+inline StoreRepresentation StoreRepresentationForC(
+    WriteBarrierKind write_barrier_kind) {
+  return StoreRepresentation(MachineTypeForC<T>(), write_barrier_kind);
+}
+
 #define DECLARE_TEMPLATE_SPECIALIZATION(ctype, mtype) \
   template <>                                         \
   inline MachineType MachineTypeForC<ctype>() {       \