Introduce a new phantom weakness type without finalization callback.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 9a881f2383ce6e6107c7c3da77f234113e62749f..389935e3b3500523becffa659883c6e94724229b 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -545,6 +545,15 @@ template <class T> class PersistentBase {
                          typename WeakCallbackInfo<P>::Callback callback,
                          WeakCallbackType type);
 
+  /**
+   * Turns this handle into a weak phantom handle without finalization callback.
+   * The handle will be reset automatically when the garbage collector detects
+   * that the object is no longer reachable.
+   * A related function Isolate::NumberOfPhantomHandleResetsSinceLastCall
+   * returns how many phantom handles were reset by the garbage collector.
+   */
+  V8_INLINE void SetWeak();
+
   template<typename P>
   V8_INLINE P* ClearWeak();
 
@@ -5784,6 +5793,12 @@ class V8_EXPORT Isolate {
       AdjustAmountOfExternalAllocatedMemory(int64_t change_in_bytes);
 
   /**
+   * Returns the number of phantom handles without callbacks that were reset
+   * by the garbage collector since the last call to this function.
+   */
+  size_t NumberOfPhantomHandleResetsSinceLastCall();
+
+  /**
    * Returns heap profiler for this isolate. Will return NULL until the isolate
    * is initialized.
    */
@@ -6628,16 +6643,17 @@ class V8_EXPORT V8 {
                                                internal::Object** handle);
   static internal::Object** CopyPersistent(internal::Object** handle);
   static void DisposeGlobal(internal::Object** global_handle);
-  static void MakeWeak(internal::Object** global_handle, void* data,
+  static void MakeWeak(internal::Object** location, void* data,
                        WeakCallbackInfo<void>::Callback weak_callback,
                        WeakCallbackType type);
-  static void MakeWeak(internal::Object** global_handle, void* data,
+  static void MakeWeak(internal::Object** location, void* data,
                        // Must be 0 or -1.
                        int internal_field_index1,
                        // Must be 1 or -1.
                        int internal_field_index2,
                        WeakCallbackInfo<void>::Callback weak_callback);
-  static void* ClearWeak(internal::Object** global_handle);
+  static void MakeWeak(internal::Object*** location_addr);
+  static void* ClearWeak(internal::Object** location);
   static void Eternalize(Isolate* isolate,
                          Value* handle,
                          int* index);
@@ -7609,6 +7625,10 @@ V8_INLINE void PersistentBase<T>::SetWeak(
                reinterpret_cast<Callback>(callback), type);
 }
 
+template <class T>
+void PersistentBase<T>::SetWeak() {
+  V8::MakeWeak(reinterpret_cast<internal::Object***>(&this->val_));
+}
 
 template <class T>
 template <typename P>