[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

src/code-factory.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_CODE_FACTORY_H_
 #define V8_CODE_FACTORY_H_
 
 #include "src/allocation.h"
 #include "src/assembler.h"
 #include "src/codegen.h"
@@ skipping 55 matching lines @@
   static Callable StoreGlobalViaContext(Isolate* isolate, int depth,
                                         LanguageMode language_mode);
 
   static Callable InstanceOf(Isolate* isolate);
 
   static Callable ToBoolean(
       Isolate* isolate, ToBooleanStub::ResultMode mode,
       ToBooleanStub::Types types = ToBooleanStub::Types());
 
   static Callable ToNumber(Isolate* isolate);
+  static Callable ToString(Isolate* isolate);
   static Callable ToObject(Isolate* isolate);
 
   static Callable StringAdd(Isolate* isolate, StringAddFlags flags,
                             PretenureFlag pretenure_flag);
 
   static Callable Typeof(Isolate* isolate);
 
   static Callable FastCloneShallowArray(Isolate* isolate);
   static Callable FastCloneShallowObject(Isolate* isolate, int length);
 
   static Callable FastNewClosure(Isolate* isolate, LanguageMode language_mode,
                                  FunctionKind kind);
 
   static Callable AllocateHeapNumber(Isolate* isolate);
 
   static Callable CallFunction(Isolate* isolate, int argc,
                                CallFunctionFlags flags);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CODE_FACTORY_H_