chromium/v8-implement-tracedreference.patch

diff -up chromium-78.0.3904.70/v8/include/v8.h.implement-tracedreference chromium-78.0.3904.70/v8/include/v8.h
--- chromium-78.0.3904.70/v8/include/v8.h.implement-tracedreference	2019-10-24 08:58:26.185640117 -0400
+++ chromium-78.0.3904.70/v8/include/v8.h	2019-10-24 09:18:33.719546481 -0400
@@ -96,6 +96,10 @@ template <class T>
 class Global;
 template <class T>
 class TracedGlobal;
+template <class T>
+class TracedReference;
+template <class T>
+class TracedReferenceBase;
 template<class K, class V, class T> class PersistentValueMap;
 template <class K, class V, class T>
 class PersistentValueMapBase;
@@ -281,7 +285,8 @@ class Local {
   V8_INLINE static Local<T> New(Isolate* isolate, Local<T> that);
   V8_INLINE static Local<T> New(Isolate* isolate,
                                 const PersistentBase<T>& that);
-  V8_INLINE static Local<T> New(Isolate* isolate, const TracedGlobal<T>& that);
+  V8_INLINE static Local<T> New(Isolate* isolate,
+                                const TracedReferenceBase<T>& that);
 
  private:
   friend class Utils;
@@ -311,7 +316,13 @@ class Local {
   template <class F>
   friend class ReturnValue;
   template <class F>
+  friend class Traced;
+  template <class F>
   friend class TracedGlobal;
+  template <class F>
+  friend class TracedReferenceBase;
+  template <class F>
+  friend class TracedReference;
 
   explicit V8_INLINE Local(T* that) : val_(that) {}
   V8_INLINE static Local<T> New(Isolate* isolate, T* that);
@@ -792,22 +803,10 @@ template <class T>
 using UniquePersistent = Global<T>;
 
 /**
- * Trait specifying behavior of |TracedGlobal<T>|.
+ * Deprecated. Use |TracedReference<T>| instead.
  */
 template <typename T>
-struct TracedGlobalTrait {
-  /**
-   * Specifies whether |TracedGlobal<T>| should clear its handle on destruction.
-   *
-   * V8 will *not* clear the embedder-side memory of the handle. The embedder is
-   * expected to report all |TracedGlobal<T>| handles through
-   * |EmbedderHeapTracer| upon garabge collection.
-   *
-   * See |EmbedderHeapTracer::IsRootForNonTracingGC| for handling with
-   * non-tracing GCs in V8.
-   */
-  static constexpr bool kRequiresExplicitDestruction = true;
-};
+struct TracedGlobalTrait {};
 
 /**
  * A traced handle with copy and move semantics. The handle is to be used
@@ -820,15 +819,131 @@ struct TracedGlobalTrait {
  *   |v8::EmbedderHeapTracer::IsRootForNonTracingGC()| whether the handle should
  *   be treated as root or not.
  *
- * For destruction semantics see |TracedGlobalTrait<T>|.
+ * Note that the base class cannot be instantiated itself. Choose from
+ * - TracedGlobal
+ * - TracedReference
  */
 template <typename T>
-class TracedGlobal {
+class TracedReferenceBase {
  public:
   /**
+   * Returns true if this TracedReferenceBase is empty, i.e., has not been
+   * assigned an object.
+   */
+  bool IsEmpty() const { return val_ == nullptr; }
+
+  /**
+   * If non-empty, destroy the underlying storage cell. |IsEmpty| will return
+   * true after this call.
+   */
+  V8_INLINE void Reset();
+
+  /**
+   * Construct a Local<T> from this handle.
+   */
+  Local<T> Get(Isolate* isolate) const { return Local<T>::New(isolate, *this); }
+
+  template <class S>
+  V8_INLINE bool operator==(const TracedReferenceBase<S>& that) const {
+    internal::Address* a = reinterpret_cast<internal::Address*>(val_);
+    internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
+    if (a == nullptr) return b == nullptr;
+    if (b == nullptr) return false;
+    return *a == *b;
+  }
+
+  template <class S>
+  V8_INLINE bool operator==(const Local<S>& that) const {
+    internal::Address* a = reinterpret_cast<internal::Address*>(val_);
+    internal::Address* b = reinterpret_cast<internal::Address*>(that.val_);
+    if (a == nullptr) return b == nullptr;
+    if (b == nullptr) return false;
+    return *a == *b;
+  }
+
+  template <class S>
+  V8_INLINE bool operator!=(const TracedReferenceBase<S>& that) const {
+    return !operator==(that);
+  }
+
+  template <class S>
+  V8_INLINE bool operator!=(const Local<S>& that) const {
+    return !operator==(that);
+  }
+
+  /**
+   * Assigns a wrapper class ID to the handle.
+   */
+  V8_INLINE void SetWrapperClassId(uint16_t class_id);
+
+  /**
+   * Returns the class ID previously assigned to this handle or 0 if no class ID
+   * was previously assigned.
+   */
+  V8_INLINE uint16_t WrapperClassId() const;
+
+  /**
+   * Adds a finalization callback to the handle. The type of this callback is
+   * similar to WeakCallbackType::kInternalFields, i.e., it will pass the
+   * parameter and the first two internal fields of the object.
+   *
+   * The callback is then supposed to reset the handle in the callback. No
+   * further V8 API may be called in this callback. In case additional work
+   * involving V8 needs to be done, a second callback can be scheduled using
+   * WeakCallbackInfo<void>::SetSecondPassCallback.
+   */
+  V8_INLINE void SetFinalizationCallback(
+      void* parameter, WeakCallbackInfo<void>::Callback callback);
+
+  template <class S>
+  V8_INLINE TracedReferenceBase<S>& As() const {
+    return reinterpret_cast<TracedReferenceBase<S>&>(
+        const_cast<TracedReferenceBase<T>&>(*this));
+  }
+
+ private:
+  enum DestructionMode { kWithDestructor, kWithoutDestructor };
+
+  /**
+   * An empty TracedReferenceBase without storage cell.
+   */
+  TracedReferenceBase() = default;
+
+  V8_INLINE static T* New(Isolate* isolate, T* that, void* slot,
+                          DestructionMode destruction_mode);
+
+  T* val_ = nullptr;
+
+  friend class EmbedderHeapTracer;
+  template <typename F>
+  friend class Local;
+  friend class Object;
+  template <typename F>
+  friend class TracedGlobal;
+  template <typename F>
+  friend class TracedReference;
+  template <typename F>
+  friend class ReturnValue;
+};
+
+/**
+ * A traced handle with destructor that clears the handle. For more details see
+ * TracedReferenceBase.
+ */
+template <typename T>
+class TracedGlobal : public TracedReferenceBase<T> {
+ public:
+  using TracedReferenceBase<T>::Reset;
+
+  /**
+   * Destructor resetting the handle.
+   */
+  ~TracedGlobal() { this->Reset(); }
+
+  /**
    * An empty TracedGlobal without storage cell.
    */
-  TracedGlobal() = default;
+  TracedGlobal() : TracedReferenceBase<T>() {}
 
   /**
    * Construct a TracedGlobal from a Local.
@@ -837,8 +952,9 @@ class TracedGlobal {
    * pointing to the same object.
    */
   template <class S>
-  TracedGlobal(Isolate* isolate, Local<S> that)
-      : val_(New(isolate, *that, &val_)) {
+  TracedGlobal(Isolate* isolate, Local<S> that) : TracedReferenceBase<T>() {
+    this->val_ = this->New(isolate, that.val_, &this->val_,
+                           TracedReferenceBase<T>::kWithDestructor);
     TYPE_CHECK(T, S);
   }
 
@@ -905,121 +1021,126 @@ class TracedGlobal {
   V8_INLINE TracedGlobal& operator=(const TracedGlobal<S>& rhs);
 
   /**
-   * Returns true if this TracedGlobal is empty, i.e., has not been assigned an
-   * object.
-   */
-  bool IsEmpty() const { return val_ == nullptr; }
-
-  /**
-   * If non-empty, destroy the underlying storage cell. |IsEmpty| will return
-   * true after this call.
-   */
-  V8_INLINE void Reset();
-
-  /**
    * If non-empty, destroy the underlying storage cell and create a new one with
    * the contents of other if other is non empty
    */
   template <class S>
   V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
 
-  /**
-   * Construct a Local<T> from this handle.
-   */
-  Local<T> Get(Isolate* isolate) const { return Local<T>::New(isolate, *this); }
-
   template <class S>
   V8_INLINE TracedGlobal<S>& As() const {
     return reinterpret_cast<TracedGlobal<S>&>(
         const_cast<TracedGlobal<T>&>(*this));
   }
+};
 
-  template <class S>
-  V8_INLINE bool operator==(const TracedGlobal<S>& that) const {
-    internal::Address* a = reinterpret_cast<internal::Address*>(**this);
-    internal::Address* b = reinterpret_cast<internal::Address*>(*that);
-    if (a == nullptr) return b == nullptr;
-    if (b == nullptr) return false;
-    return *a == *b;
-  }
+/**
+ * A traced handle without destructor that clears the handle. The embedder needs
+ * to ensure that the handle is not accessed once the V8 object has been
+ * reclaimed. This can happen when the handle is not passed through the
+ * EmbedderHeapTracer. For more details see TracedReferenceBase.
+ */
+template <typename T>
+class TracedReference : public TracedReferenceBase<T> {
+ public:
+  using TracedReferenceBase<T>::Reset;
+
+  /**
+   * An empty TracedReference without storage cell.
+   */
+  TracedReference() : TracedReferenceBase<T>() {}
 
+  /**
+   * Construct a TracedReference from a Local.
+   *
+   * When the Local is non-empty, a new storage cell is created
+   * pointing to the same object.
+   */
   template <class S>
-  V8_INLINE bool operator==(const Local<S>& that) const {
-    internal::Address* a = reinterpret_cast<internal::Address*>(**this);
-    internal::Address* b = reinterpret_cast<internal::Address*>(*that);
-    if (a == nullptr) return b == nullptr;
-    if (b == nullptr) return false;
-    return *a == *b;
+  TracedReference(Isolate* isolate, Local<S> that) : TracedReferenceBase<T>() {
+    this->val_ = this->New(isolate, that.val_, &this->val_,
+                           TracedReferenceBase<T>::kWithoutDestructor);
+    TYPE_CHECK(T, S);
   }
 
-  template <class S>
-  V8_INLINE bool operator!=(const TracedGlobal<S>& that) const {
-    return !operator==(that);
+  /**
+   * Move constructor initializing TracedReference from an
+   * existing one.
+   */
+  V8_INLINE TracedReference(TracedReference&& other) {
+    // Forward to operator=.
+    *this = std::move(other);
   }
 
-  template <class S>
-  V8_INLINE bool operator!=(const Local<S>& that) const {
-    return !operator==(that);
+  /**
+   * Move constructor initializing TracedReference from an
+   * existing one.
+   */
+  template <typename S>
+  V8_INLINE TracedReference(TracedReference<S>&& other) {
+    // Forward to operator=.
+    *this = std::move(other);
   }
 
   /**
-   * Assigns a wrapper class ID to the handle.
+   * Copy constructor initializing TracedReference from an
+   * existing one.
    */
-  V8_INLINE void SetWrapperClassId(uint16_t class_id);
+  V8_INLINE TracedReference(const TracedReference& other) {
+    // Forward to operator=;
+    *this = other;
+  }
 
   /**
-   * Returns the class ID previously assigned to this handle or 0 if no class ID
-   * was previously assigned.
+   * Copy constructor initializing TracedReference from an
+   * existing one.
    */
-  V8_INLINE uint16_t WrapperClassId() const;
+  template <typename S>
+  V8_INLINE TracedReference(const TracedReference<S>& other) {
+    // Forward to operator=;
+    *this = other;
+  }
 
   /**
-   * Adds a finalization callback to the handle. The type of this callback is
-   * similar to WeakCallbackType::kInternalFields, i.e., it will pass the
-   * parameter and the first two internal fields of the object.
-   *
-   * The callback is then supposed to reset the handle in the callback. No
-   * further V8 API may be called in this callback. In case additional work
-   * involving V8 needs to be done, a second callback can be scheduled using
-   * WeakCallbackInfo<void>::SetSecondPassCallback.
+   * Move assignment operator initializing TracedGlobal from an existing one.
    */
-  V8_INLINE void SetFinalizationCallback(
-      void* parameter, WeakCallbackInfo<void>::Callback callback);
+  V8_INLINE TracedReference& operator=(TracedReference&& rhs);
 
- private:
-  // Wrapping type used when clearing on destruction is required.
-  struct WrappedForDestruction {
-    T* value;
-
-    explicit WrappedForDestruction(T* val) : value(val) {}
-    ~WrappedForDestruction();
-    operator T*() const { return value; }
-    T* operator*() const { return value; }
-    T* operator->() const { return value; }
-    WrappedForDestruction& operator=(const WrappedForDestruction& other) {
-      value = other.value;
-      return *this;
-    }
-    WrappedForDestruction& operator=(T* val) {
-      value = val;
-      return *this;
-    }
-  };
+  /**
+   * Move assignment operator initializing TracedGlobal from an existing one.
+   */
+  template <class S>
+  V8_INLINE TracedReference& operator=(TracedReference<S>&& rhs);
 
-  V8_INLINE static T* New(Isolate* isolate, T* that, void* slot);
+  /**
+   * Copy assignment operator initializing TracedGlobal from an existing one.
+   *
+   * Note: Prohibited when |other| has a finalization callback set through
+   * |SetFinalizationCallback|.
+   */
+  V8_INLINE TracedReference& operator=(const TracedReference& rhs);
 
-  T* operator*() const { return this->val_; }
+  /**
+   * Copy assignment operator initializing TracedGlobal from an existing one.
+   *
+   * Note: Prohibited when |other| has a finalization callback set through
+   * |SetFinalizationCallback|.
+   */
+  template <class S>
+  V8_INLINE TracedReference& operator=(const TracedReference<S>& rhs);
 
-  typename std::conditional<
-      TracedGlobalTrait<TracedGlobal<T>>::kRequiresExplicitDestruction,
-      WrappedForDestruction, T*>::type val_{nullptr};
+  /**
+   * If non-empty, destroy the underlying storage cell and create a new one with
+   * the contents of other if other is non empty
+   */
+  template <class S>
+  V8_INLINE void Reset(Isolate* isolate, const Local<S>& other);
 
-  friend class EmbedderHeapTracer;
-  template <typename F>
-  friend class Local;
-  friend class Object;
-  template <typename F>
-  friend class ReturnValue;
+  template <class S>
+  V8_INLINE TracedReference<S>& As() const {
+    return reinterpret_cast<TracedReference<S>&>(
+        const_cast<TracedReference<T>&>(*this));
+  }
 };
 
  /**
@@ -3640,8 +3761,9 @@ class V8_EXPORT Object : public Value {
     return object.val_->InternalFieldCount();
   }
 
-  /** Same as above, but works for TracedGlobal. */
-  V8_INLINE static int InternalFieldCount(const TracedGlobal<Object>& object) {
+  /** Same as above, but works for TracedReferenceBase. */
+  V8_INLINE static int InternalFieldCount(
+      const TracedReferenceBase<Object>& object) {
     return object.val_->InternalFieldCount();
   }
 
@@ -3666,7 +3788,7 @@ class V8_EXPORT Object : public Value {
 
   /** Same as above, but works for TracedGlobal. */
   V8_INLINE static void* GetAlignedPointerFromInternalField(
-      const TracedGlobal<Object>& object, int index) {
+      const TracedReferenceBase<Object>& object, int index) {
     return object.val_->GetAlignedPointerFromInternalField(index);
   }
 
@@ -3956,7 +4078,7 @@ class ReturnValue {
   template <typename S>
   V8_INLINE void Set(const Global<S>& handle);
   template <typename S>
-  V8_INLINE void Set(const TracedGlobal<S>& handle);
+  V8_INLINE void Set(const TracedReferenceBase<S>& handle);
   template <typename S>
   V8_INLINE void Set(const Local<S> handle);
   // Fast primitive setters
@@ -7376,7 +7498,8 @@ class V8_EXPORT EmbedderHeapTracer {
   class V8_EXPORT TracedGlobalHandleVisitor {
    public:
     virtual ~TracedGlobalHandleVisitor() = default;
-    virtual void VisitTracedGlobalHandle(const TracedGlobal<Value>& value) = 0;
+    virtual void VisitTracedGlobalHandle(const TracedGlobal<Value>& handle) {}
+    virtual void VisitTracedReference(const TracedReference<Value>& handle) {}
   };
 
   /**
@@ -7414,7 +7537,7 @@ class V8_EXPORT EmbedderHeapTracer {
   virtual void RegisterV8References(
       const std::vector<std::pair<void*, void*> >& embedder_fields) = 0;
 
-  void RegisterEmbedderReference(const TracedGlobal<v8::Value>& ref);
+  void RegisterEmbedderReference(const TracedReferenceBase<v8::Value>& ref);
 
   /**
    * Called at the beginning of a GC cycle.
@@ -7475,32 +7598,35 @@ class V8_EXPORT EmbedderHeapTracer {
    *
    * If this returns false, then V8 may decide that the object referred to by
    * such a handle is reclaimed. In that case:
-   * - No action is required if handles are used with destructors.
-   * - When run without destructors (by specializing
-   * |TracedGlobalTrait::kRequiresExplicitDestruction|) V8 calls
-   * |ResetHandleInNonTracingGC|.
-   *
-   * Note that the |handle| is different from the |TracedGlobal<T>| handle that
-   * the embedder holds for retaining the object. The embedder may use
-   * |TracedGlobal<T>::WrapperClassId()| to distinguish cases where it wants
-   * handles to be treated as roots from not being treated as roots.
+   * - No action is required if handles are used with destructors, i.e., by just
+   * using |TracedGlobal|.
+   * - When run without destructors, i.e., by using
+   * |TracedReference|, V8 calls |ResetHandleInNonTracingGC|.
+   *
+   * Note that the |handle| is different from the handle that the embedder holds
+   * for retaining the object. The embedder may use |WrapperClassId()| to
+   * distinguish cases where it wants handles to be treated as roots from not
+   * being treated as roots.
    */
   virtual bool IsRootForNonTracingGC(
-      const v8::TracedGlobal<v8::Value>& handle) {
-    return true;
-  }
+      const v8::TracedReference<v8::Value>& handle);
+  virtual bool IsRootForNonTracingGC(const v8::TracedGlobal<v8::Value>& handle);
 
   /**
    * Used in combination with |IsRootForNonTracingGC|. Called by V8 when an
    * object that is backed by a handle is reclaimed by a non-tracing garbage
    * collection. It is up to the embedder to reset the original handle.
    *
-   * Note that the |handle| is different from the |TracedGlobal<T>| handle that
-   * the embedder holds for retaining the object. It is up to the embedder to
-   * find the orignal |TracedGlobal<T>| handle via the object or class id.
+   * Note that the |handle| is different from the handle that the embedder holds
+   * for retaining the object. It is up to the embedder to find the original
+   * handle via the object or class id.
    */
   virtual void ResetHandleInNonTracingGC(
-      const v8::TracedGlobal<v8::Value>& handle) {}
+      const v8::TracedReference<v8::Value>& handle);
+  V8_DEPRECATE_SOON(
+      "Use TracedReference version when not requiring destructors.",
+      virtual void ResetHandleInNonTracingGC(
+          const v8::TracedGlobal<v8::Value>& handle));
 
   /*
    * Called by the embedder to immediately perform a full garbage collection.
@@ -9103,8 +9229,12 @@ class V8_EXPORT V8 {
   template <class T>
   friend class Maybe;
   template <class T>
+  friend class TracedReferenceBase;
+  template <class T>
   friend class TracedGlobal;
   template <class T>
+  friend class TracedReference;
+  template <class T>
   friend class WeakCallbackInfo;
   template <class T> friend class Eternal;
   template <class T> friend class PersistentBase;
@@ -9975,7 +10105,7 @@ Local<T> Local<T>::New(Isolate* isolate,
 }
 
 template <class T>
-Local<T> Local<T>::New(Isolate* isolate, const TracedGlobal<T>& that) {
+Local<T> Local<T>::New(Isolate* isolate, const TracedReferenceBase<T>& that) {
   return New(isolate, that.val_);
 }
 
@@ -10156,26 +10286,20 @@ Global<T>& Global<T>::operator=(Global<S
 }
 
 template <class T>
-TracedGlobal<T>::WrappedForDestruction::~WrappedForDestruction() {
-  if (value == nullptr) return;
-  V8::DisposeTracedGlobal(reinterpret_cast<internal::Address*>(value));
-  value = nullptr;
-}
-
-template <class T>
-T* TracedGlobal<T>::New(Isolate* isolate, T* that, void* slot) {
+T* TracedReferenceBase<T>::New(Isolate* isolate, T* that, void* slot,
+                               DestructionMode destruction_mode) {
   if (that == nullptr) return nullptr;
   internal::Address* p = reinterpret_cast<internal::Address*>(that);
   return reinterpret_cast<T*>(V8::GlobalizeTracedReference(
       reinterpret_cast<internal::Isolate*>(isolate), p,
       reinterpret_cast<internal::Address*>(slot),
-      TracedGlobalTrait<TracedGlobal<T>>::kRequiresExplicitDestruction));
+      destruction_mode == kWithDestructor));
 }
 
 template <class T>
-void TracedGlobal<T>::Reset() {
+void TracedReferenceBase<T>::Reset() {
   if (IsEmpty()) return;
-  V8::DisposeTracedGlobal(reinterpret_cast<internal::Address*>(**this));
+  V8::DisposeTracedGlobal(reinterpret_cast<internal::Address*>(val_));
   val_ = nullptr;
 }
 
@@ -10185,7 +10309,8 @@ void TracedGlobal<T>::Reset(Isolate* iso
   TYPE_CHECK(T, S);
   Reset();
   if (other.IsEmpty()) return;
-  this->val_ = New(isolate, other.val_, &val_);
+  this->val_ = this->New(isolate, other.val_, &this->val_,
+                         TracedReferenceBase<T>::kWithDestructor);
 }
 
 template <class T>
@@ -10233,28 +10358,83 @@ TracedGlobal<T>& TracedGlobal<T>::operat
 }
 
 template <class T>
-void TracedGlobal<T>::SetWrapperClassId(uint16_t class_id) {
+template <class S>
+void TracedReference<T>::Reset(Isolate* isolate, const Local<S>& other) {
+  TYPE_CHECK(T, S);
+  Reset();
+  if (other.IsEmpty()) return;
+  this->val_ = this->New(isolate, other.val_, &this->val_,
+                         TracedReferenceBase<T>::kWithoutDestructor);
+}
+
+template <class T>
+template <class S>
+TracedReference<T>& TracedReference<T>::operator=(TracedReference<S>&& rhs) {
+  TYPE_CHECK(T, S);
+  *this = std::move(rhs.template As<T>());
+  return *this;
+}
+
+template <class T>
+template <class S>
+TracedReference<T>& TracedReference<T>::operator=(
+    const TracedReference<S>& rhs) {
+  TYPE_CHECK(T, S);
+  *this = rhs.template As<T>();
+  return *this;
+}
+
+template <class T>
+TracedReference<T>& TracedReference<T>::operator=(TracedReference&& rhs) {
+  if (this != &rhs) {
+    this->Reset();
+    if (rhs.val_ != nullptr) {
+      this->val_ = rhs.val_;
+      V8::MoveTracedGlobalReference(
+          reinterpret_cast<internal::Address**>(&rhs.val_),
+          reinterpret_cast<internal::Address**>(&this->val_));
+      rhs.val_ = nullptr;
+    }
+  }
+  return *this;
+}
+
+template <class T>
+TracedReference<T>& TracedReference<T>::operator=(const TracedReference& rhs) {
+  if (this != &rhs) {
+    this->Reset();
+    if (rhs.val_ != nullptr) {
+      V8::CopyTracedGlobalReference(
+          reinterpret_cast<const internal::Address* const*>(&rhs.val_),
+          reinterpret_cast<internal::Address**>(&this->val_));
+    }
+  }
+  return *this;
+}
+
+template <class T>
+void TracedReferenceBase<T>::SetWrapperClassId(uint16_t class_id) {
   typedef internal::Internals I;
   if (IsEmpty()) return;
-  internal::Address* obj = reinterpret_cast<internal::Address*>(**this);
+  internal::Address* obj = reinterpret_cast<internal::Address*>(val_);
   uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
   *reinterpret_cast<uint16_t*>(addr) = class_id;
 }
 
 template <class T>
-uint16_t TracedGlobal<T>::WrapperClassId() const {
+uint16_t TracedReferenceBase<T>::WrapperClassId() const {
   typedef internal::Internals I;
   if (IsEmpty()) return 0;
-  internal::Address* obj = reinterpret_cast<internal::Address*>(**this);
+  internal::Address* obj = reinterpret_cast<internal::Address*>(val_);
   uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + I::kNodeClassIdOffset;
   return *reinterpret_cast<uint16_t*>(addr);
 }
 
 template <class T>
-void TracedGlobal<T>::SetFinalizationCallback(
+void TracedReferenceBase<T>::SetFinalizationCallback(
     void* parameter, typename WeakCallbackInfo<void>::Callback callback) {
-  V8::SetFinalizationCallbackTraced(
-      reinterpret_cast<internal::Address*>(**this), parameter, callback);
+  V8::SetFinalizationCallbackTraced(reinterpret_cast<internal::Address*>(val_),
+                                    parameter, callback);
 }
 
 template <typename T>
@@ -10273,12 +10453,12 @@ void ReturnValue<T>::Set(const Global<S>
 
 template <typename T>
 template <typename S>
-void ReturnValue<T>::Set(const TracedGlobal<S>& handle) {
+void ReturnValue<T>::Set(const TracedReferenceBase<S>& handle) {
   TYPE_CHECK(T, S);
   if (V8_UNLIKELY(handle.IsEmpty())) {
     *value_ = GetDefaultValue();
   } else {
-    *value_ = *reinterpret_cast<internal::Address*>(*handle);
+    *value_ = *reinterpret_cast<internal::Address*>(handle.val_);
   }
 }
 
diff -up chromium-78.0.3904.70/v8/src/api/api.cc.implement-tracedreference chromium-78.0.3904.70/v8/src/api/api.cc
--- chromium-78.0.3904.70/v8/src/api/api.cc.implement-tracedreference	2019-10-24 09:18:56.712105100 -0400
+++ chromium-78.0.3904.70/v8/src/api/api.cc	2019-10-24 09:20:17.428555637 -0400
@@ -10346,11 +10346,12 @@ void EmbedderHeapTracer::DecreaseAllocat
 }
 
 void EmbedderHeapTracer::RegisterEmbedderReference(
-    const TracedGlobal<v8::Value>& ref) {
+    const TracedReferenceBase<v8::Value>& ref) {
   if (ref.IsEmpty()) return;
 
   i::Heap* const heap = reinterpret_cast<i::Isolate*>(isolate_)->heap();
-  heap->RegisterExternallyReferencedObject(reinterpret_cast<i::Address*>(*ref));
+  heap->RegisterExternallyReferencedObject(
+      reinterpret_cast<i::Address*>(ref.val_));
 }
 
 void EmbedderHeapTracer::IterateTracedGlobalHandles(
@@ -10360,6 +10361,26 @@ void EmbedderHeapTracer::IterateTracedGl
   isolate->global_handles()->IterateTracedNodes(visitor);
 }
 
+bool EmbedderHeapTracer::IsRootForNonTracingGC(
+    const v8::TracedReference<v8::Value>& handle) {
+  return true;
+}
+
+bool EmbedderHeapTracer::IsRootForNonTracingGC(
+    const v8::TracedGlobal<v8::Value>& handle) {
+  return true;
+}
+
+void EmbedderHeapTracer::ResetHandleInNonTracingGC(
+    const v8::TracedReference<v8::Value>& handle) {
+  UNREACHABLE();
+}
+
+void EmbedderHeapTracer::ResetHandleInNonTracingGC(
+    const v8::TracedGlobal<v8::Value>& handle) {
+  UNREACHABLE();
+}
+
 namespace internal {
 
 const size_t HandleScopeImplementer::kEnteredContextsOffset =
diff -up chromium-78.0.3904.70/v8/src/handles/global-handles.cc.implement-tracedreference chromium-78.0.3904.70/v8/src/handles/global-handles.cc
--- chromium-78.0.3904.70/v8/src/handles/global-handles.cc.implement-tracedreference	2019-10-24 09:20:39.954123225 -0400
+++ chromium-78.0.3904.70/v8/src/handles/global-handles.cc	2019-10-24 09:21:45.911857072 -0400
@@ -901,8 +901,13 @@ void GlobalHandles::IdentifyWeakUnmodifi
       DCHECK(node->is_root());
       if (is_unmodified(node->location())) {
         v8::Value* value = ToApi<v8::Value>(node->handle());
-        node->set_root(tracer->IsRootForNonTracingGC(
-            *reinterpret_cast<v8::TracedGlobal<v8::Value>*>(&value)));
+        if (node->has_destructor()) {
+          node->set_root(tracer->IsRootForNonTracingGC(
+              *reinterpret_cast<v8::TracedGlobal<v8::Value>*>(&value)));
+        } else {
+          node->set_root(tracer->IsRootForNonTracingGC(
+              *reinterpret_cast<v8::TracedReference<v8::Value>*>(&value)));
+        }
       }
     }
   }
@@ -990,7 +995,7 @@ void GlobalHandles::IterateYoungWeakUnmo
         } else {
           v8::Value* value = ToApi<v8::Value>(node->handle());
           tracer->ResetHandleInNonTracingGC(
-              *reinterpret_cast<v8::TracedGlobal<v8::Value>*>(&value));
+              *reinterpret_cast<v8::TracedReference<v8::Value>*>(&value));
           DCHECK(!node->IsInUse());
         }
 
@@ -1271,8 +1276,13 @@ void GlobalHandles::IterateTracedNodes(
   for (TracedNode* node : *traced_nodes_) {
     if (node->IsInUse()) {
       v8::Value* value = ToApi<v8::Value>(node->handle());
-      visitor->VisitTracedGlobalHandle(
-          *reinterpret_cast<v8::TracedGlobal<v8::Value>*>(&value));
+      if (node->has_destructor()) {
+        visitor->VisitTracedGlobalHandle(
+            *reinterpret_cast<v8::TracedGlobal<v8::Value>*>(&value));
+      } else {
+        visitor->VisitTracedReference(
+            *reinterpret_cast<v8::TracedReference<v8::Value>*>(&value));
+      }
     }
   }
 }
diff -up chromium-78.0.3904.70/v8/src/heap/embedder-tracing.h.implement-tracedreference chromium-78.0.3904.70/v8/src/heap/embedder-tracing.h
--- chromium-78.0.3904.70/v8/src/heap/embedder-tracing.h.implement-tracedreference	2019-10-24 09:22:03.664519559 -0400
+++ chromium-78.0.3904.70/v8/src/heap/embedder-tracing.h	2019-10-24 09:22:45.197729964 -0400
@@ -57,7 +57,12 @@ class V8_EXPORT_PRIVATE LocalEmbedderHea
   bool IsRootForNonTracingGC(const v8::TracedGlobal<v8::Value>& handle) {
     return !InUse() || remote_tracer_->IsRootForNonTracingGC(handle);
   }
-  void ResetHandleInNonTracingGC(const v8::TracedGlobal<v8::Value>& handle) {
+
+  bool IsRootForNonTracingGC(const v8::TracedReference<v8::Value>& handle) {
+    return !InUse() || remote_tracer_->IsRootForNonTracingGC(handle);
+  }
+
+  void ResetHandleInNonTracingGC(const v8::TracedReference<v8::Value>& handle) {
     // Resetting is only called when IsRootForNonTracingGC returns false which
     // can only happen the EmbedderHeapTracer is set on API level.
     DCHECK(InUse());