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

src/x64/macro-assembler-x64.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_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/base/flags.h"
 #include "src/frames.h"
 #include "src/globals.h"
 #include "src/x64/frames-x64.h"
 
 namespace v8 {
 namespace internal {
 
 // Give alias names to registers for calling conventions.
 const Register kReturnRegister0 = {Register::kCode_rax};
 const Register kReturnRegister1 = {Register::kCode_rdx};
+const Register kReturnRegister2 = {Register::kCode_r8};
 const Register kJSFunctionRegister = {Register::kCode_rdi};
 const Register kContextRegister = {Register::kCode_rsi};
 const Register kInterpreterAccumulatorRegister = {Register::kCode_rax};
 const Register kInterpreterRegisterFileRegister = {Register::kCode_r11};
 const Register kInterpreterBytecodeOffsetRegister = {Register::kCode_r12};
 const Register kInterpreterBytecodeArrayRegister = {Register::kCode_r14};
 const Register kInterpreterDispatchTableRegister = {Register::kCode_r15};
 const Register kJavaScriptCallArgCountRegister = {Register::kCode_rax};
 const Register kJavaScriptCallNewTargetRegister = {Register::kCode_rdx};
 const Register kRuntimeCallFunctionRegister = {Register::kCode_rbx};
@@ skipping 1708 matching lines @@
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_