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

src/arm/macro-assembler-arm.h

Index: src/arm/macro-assembler-arm.h
diff --git a/src/arm/macro-assembler-arm.h b/src/arm/macro-assembler-arm.h
index 26811b988cfe5efdc1b08582694d0d6987531374..ff7891081d56dca642604feff156c74382c4817a 100644
--- a/src/arm/macro-assembler-arm.h
+++ b/src/arm/macro-assembler-arm.h
@@ -16,6 +16,7 @@ namespace internal {
 // Give alias names to registers for calling conventions.
 const Register kReturnRegister0 = {Register::kCode_r0};
 const Register kReturnRegister1 = {Register::kCode_r1};
+const Register kReturnRegister2 = {Register::kCode_r2};
 const Register kJSFunctionRegister = {Register::kCode_r1};
 const Register kContextRegister = {Register::kCode_r7};
 const Register kInterpreterAccumulatorRegister = {Register::kCode_r0};