[stubs] Further optimize Load/StoreGlobalViaContext stubs.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index d8852427613ce939b7542b209bb5f39b0a522d63..d29d2cf7de2fce665eaf9fc1db406da70c286d15 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3988,6 +3988,9 @@ class ScopeInfo : public FixedArray {
                               InitializationFlag* init_flag,
                               MaybeAssignedFlag* maybe_assigned_flag);
 
+  // Lookup the name of a certain context slot by its index.
+  String* ContextSlotName(int slot_index);
+
   // Lookup support for serialized scope info. Returns the
   // parameter index for a given parameter name if the parameter is present;
   // otherwise returns a value < 0. The name must be an internalized string.