[es6] Implement spec compliant ToPrimitive in the runtime.

src/json-stringifier.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_JSON_STRINGIFIER_H_
 #define V8_JSON_STRINGIFIER_H_
 
 #include "src/conversions.h"
 #include "src/lookup.h"
 #include "src/messages.h"
@@ skipping 364 matching lines @@
   return SUCCESS;
 }
 
 
 BasicJsonStringifier::Result BasicJsonStringifier::SerializeJSValue(
     Handle<JSValue> object) {
   String* class_name = object->class_name();
   if (class_name == isolate_->heap()->String_string()) {
     Handle<Object> value;
     ASSIGN_RETURN_ON_EXCEPTION_VALUE(
-        isolate_, value, Execution::ToString(isolate_, object), EXCEPTION);
+        isolate_, value, Object::ToString(isolate_, object), EXCEPTION);
     SerializeString(Handle<String>::cast(value));
   } else if (class_name == isolate_->heap()->Number_string()) {
     Handle<Object> value;
     ASSIGN_RETURN_ON_EXCEPTION_VALUE(
-        isolate_, value, Execution::ToNumber(isolate_, object), EXCEPTION);
+        isolate_, value, Object::ToNumber(isolate_, object), EXCEPTION);
     if (value->IsSmi()) return SerializeSmi(Smi::cast(*value));
     SerializeHeapNumber(Handle<HeapNumber>::cast(value));
   } else if (class_name == isolate_->heap()->Boolean_string()) {
     Object* value = JSValue::cast(*object)->value();
     DCHECK(value->IsBoolean());
     builder_.AppendCString(value->IsTrue() ? "true" : "false");
   } else {
     // Fail gracefully for special value wrappers.
     isolate_->ThrowIllegalOperation();
     return EXCEPTION;
@@ skipping 270 matching lines @@
       SerializeString_<uint8_t, uc16>(object);
     } else {
       SerializeString_<uc16, uc16>(object);
     }
   }
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_JSON_STRINGIFIER_H_