Give v8::Eternal a direct reference to the handle.

src/api.cc

 // 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.
 
 #include "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 930 matching lines @@
 }
 
 void* V8::ClearWeak(i::Object** location) {
   return i::GlobalHandles::ClearWeakness(location);
 }
 
 void V8::DisposeGlobal(i::Object** location) {
   i::GlobalHandles::Destroy(location);
 }
 
-
-void V8::Eternalize(Isolate* v8_isolate, Value* value, int* index) {
+Value* V8::Eternalize(Isolate* v8_isolate, Value* value) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(v8_isolate);
   i::Object* object = *Utils::OpenHandle(value);
-  isolate->eternal_handles()->Create(isolate, object, index);
+  int index = -1;
+  isolate->eternal_handles()->Create(isolate, object, &index);
+  return reinterpret_cast<Value*>(
+      isolate->eternal_handles()->Get(index).location());
 }
 
 
-Local<Value> V8::GetEternal(Isolate* v8_isolate, int index) {
-  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(v8_isolate);
-  return Utils::ToLocal(isolate->eternal_handles()->Get(index));
-}
-
-
 void V8::FromJustIsNothing() {
   Utils::ApiCheck(false, "v8::FromJust", "Maybe value is Nothing.");
 }
 
 
 void V8::ToLocalEmpty() {
   Utils::ApiCheck(false, "v8::ToLocalChecked", "Empty MaybeLocal.");
 }
 
 void V8::InternalFieldOutOfBounds(int index) {
@@ skipping 9271 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8