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

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 36f00a7da1a53f75f841b80a4519d411deb347a5..fd7b16134b4ba645212b86adf45f77e99d417f45 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -814,9 +814,14 @@ class ExternalReference BASE_EMBEDDED {
   // Used in the simulator to support different native api calls.
   enum Type {
     // Builtin call.
-    // Object* f(v8::internal::Arguments).
+    // Object* f(v8::internal::Arguments) or
+    // ObjectPair f(v8::internal::Arguments).
     BUILTIN_CALL,  // default
 
+    // Builtin call that returns .
+    // ObjectTriple f(v8::internal::Arguments).
+    BUILTIN_CALL_TRIPLE,
+
     // Builtin that takes float arguments and returns an int.
     // int f(double, double).
     BUILTIN_COMPARE_CALL,