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

src/mips64/macro-assembler-mips64.h

Index: src/mips64/macro-assembler-mips64.h
diff --git a/src/mips64/macro-assembler-mips64.h b/src/mips64/macro-assembler-mips64.h
index 31ed8a32e118e0dc1c2466d49267eade9ace75a9..acb336dfac9170ac768634857e62e5a697127195 100644
--- a/src/mips64/macro-assembler-mips64.h
+++ b/src/mips64/macro-assembler-mips64.h
@@ -15,6 +15,7 @@ namespace internal {
 // Give alias names to registers for calling conventions.
 const Register kReturnRegister0 = {Register::kCode_v0};
 const Register kReturnRegister1 = {Register::kCode_v1};
+const Register kReturnRegister2 = {Register::kCode_a0};
 const Register kJSFunctionRegister = {Register::kCode_a1};
 const Register kContextRegister = {Register::kCpRegister};
 const Register kInterpreterAccumulatorRegister = {Register::kCode_v0};