[Interpreter]: Add kRegList operand type for register list operands.

src/interpreter/bytecode-register.cc

 // Copyright 2015 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.
 
 #include "src/interpreter/bytecode-register.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
@@ skipping 103 matching lines @@
   }
   if (reg4.is_valid() && reg3.index() + 1 != reg4.index()) {
     return false;
   }
   if (reg5.is_valid() && reg4.index() + 1 != reg5.index()) {
     return false;
   }
   return true;
 }
 
-std::string Register::ToString(int parameter_count) {
+std::string Register::ToString(int parameter_count) const {
   if (is_current_context()) {
     return std::string("<context>");
   } else if (is_function_closure()) {
     return std::string("<closure>");
   } else if (is_new_target()) {
     return std::string("<new.target>");
   } else if (is_parameter()) {
     int parameter_index = ToParameterIndex(parameter_count);
     if (parameter_index == 0) {
       return std::string("<this>");
     } else {
       std::ostringstream s;
       s << "a" << parameter_index - 1;
       return s.str();
     }
   } else {
     std::ostringstream s;
     s << "r" << index();
     return s.str();
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8