[Interpreter] Add ForInPrepare runtime function which returns a ObjectTriple.

src/arguments.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARGUMENTS_H_
 #define V8_ARGUMENTS_H_
 
 #include "src/allocation.h"
 #include "src/isolate.h"
 
@@ skipping 267 matching lines @@
   CLOBBER_DOUBLE_REGISTERS();                                            \
   Arguments args(args_length, args_object);                              \
   return __RT_impl_##Name(args, isolate);                                \
 }                                                                        \
 static Type __RT_impl_##Name(Arguments args, Isolate* isolate)
 
 
 #define RUNTIME_FUNCTION(Name) RUNTIME_FUNCTION_RETURNS_TYPE(Object*, Name)
 #define RUNTIME_FUNCTION_RETURN_PAIR(Name) \
     RUNTIME_FUNCTION_RETURNS_TYPE(ObjectPair, Name)
+#define RUNTIME_FUNCTION_RETURN_TRIPLE(Name) \
+    RUNTIME_FUNCTION_RETURNS_TYPE(ObjectTriple, Name)
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARGUMENTS_H_