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diff --git a/dom/indexedDB/SafeRefPtr.h b/dom/indexedDB/SafeRefPtr.h
new file mode 100644
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+++ b/dom/indexedDB/SafeRefPtr.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_saferefptr_h__
+#define mozilla_saferefptr_h__
+
+#include "mozilla/ArrayAlgorithm.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/RefCounted.h"
+#include "mozilla/RefPtr.h"
+#include "nsCOMPtr.h"
+#include "nsTObserverArray.h"
+
+namespace mozilla {
+template <typename T>
+class SafeRefPtr;
+
+template <typename T, typename... Args>
+SafeRefPtr<T> MakeSafeRefPtr(Args&&... aArgs);
+
+namespace detail {
+struct InitialConstructionTag {};
+
+class SafeRefCountedBase {
+  template <typename U, typename... Args>
+  friend SafeRefPtr<U> mozilla::MakeSafeRefPtr(Args&&... aArgs);
+
+  template <typename T>
+  friend class SafeRefPtr;
+
+  void* operator new(size_t aSize) { return ::operator new(aSize); }
+
+ protected:
+  void operator delete(void* aPtr) { ::operator delete(aPtr); }
+
+ public:
+  void* operator new[](size_t) = delete;
+};
+
+// SafeRefCounted is similar to RefCounted, but they differ in their initial
+// refcount (here 1), and the visibility of operator new (here private). The
+// rest is mostly a copy of RefCounted.
+template <typename T, RefCountAtomicity Atomicity>
+class SafeRefCounted : public SafeRefCountedBase {
+ protected:
+  SafeRefCounted() = default;
+#ifdef DEBUG
+  ~SafeRefCounted() { MOZ_ASSERT(mRefCnt == detail::DEAD); }
+#endif
+
+ public:
+  // Compatibility with nsRefPtr.
+  MozRefCountType AddRef() const {
+    // Note: this method must be thread safe for AtomicRefCounted.
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0);
+    const MozRefCountType cnt = ++mRefCnt;
+    detail::RefCountLogger::logAddRef(static_cast<const T*>(this), cnt);
+    return cnt;
+  }
+
+  MozRefCountType Release() const {
+    // Note: this method must be thread safe for AtomicRefCounted.
+    MOZ_ASSERT(int32_t(mRefCnt) > 0);
+    detail::RefCountLogger::ReleaseLogger logger(static_cast<const T*>(this));
+    const MozRefCountType cnt = --mRefCnt;
+    // Note: it's not safe to touch |this| after decrementing the refcount,
+    // except for below.
+    logger.logRelease(cnt);
+    if (0 == cnt) {
+      // Because we have atomically decremented the refcount above, only
+      // one thread can get a 0 count here, so as long as we can assume that
+      // everything else in the system is accessing this object through
+      // RefPtrs, it's safe to access |this| here.
+#ifdef DEBUG
+      mRefCnt = detail::DEAD;
+#endif
+      delete static_cast<const T*>(this);
+    }
+    return cnt;
+  }
+
+  // Compatibility with wtf::RefPtr.
+  void ref() { AddRef(); }
+  void deref() { Release(); }
+  MozRefCountType refCount() const { return mRefCnt; }
+  bool hasOneRef() const {
+    MOZ_ASSERT(mRefCnt > 0);
+    return mRefCnt == 1;
+  }
+
+ protected:
+  SafeRefPtr<T> SafeRefPtrFromThis();
+
+ private:
+  mutable RC<MozRefCountType, Atomicity> mRefCnt =
+      RC<MozRefCountType, Atomicity>{1};
+};
+}  // namespace detail
+
+template <typename T>
+class SafeRefCounted
+    : public detail::SafeRefCounted<T, detail::NonAtomicRefCount> {
+ public:
+  ~SafeRefCounted() {
+    static_assert(std::is_base_of<SafeRefCounted, T>::value,
+                  "T must derive from SafeRefCounted<T>");
+  }
+};
+
+template <typename T>
+class AtomicSafeRefCounted
+    : public detail::SafeRefCounted<T, detail::AtomicRefCount> {
+ public:
+  ~AtomicSafeRefCounted() {
+    static_assert(std::is_base_of<AtomicSafeRefCounted, T>::value,
+                  "T must derive from AtomicSafeRefCounted<T>");
+  }
+};
+
+struct AcquireStrongRefFromRawPtr {};
+
+// XXX for Apple, clang::trivial_abi is probably also supported, but we need to
+// find out the correct version number
+#if defined(__clang__) && !defined(__apple_build_version__) && \
+    __clang_major__ >= 7
+#  define MOZ_TRIVIAL_ABI [[clang::trivial_abi]]
+#else
+#  define MOZ_TRIVIAL_ABI
+#endif
+
+// A restricted variant of mozilla::RefPtr<T>, which prohibits some unsafe or
+// unperformant misuses, in particular:
+// * It is not implicitly convertible from a raw pointer. Unsafe acquisitions
+//   from a raw pointer must be made using the verbose
+//   AcquireStrongRefFromRawPtr. To create a new object on the heap, use
+//   MakeSafeRefPtr.
+// * It does not implicitly decay to a raw pointer. unsafeGetRawPtr() must be
+// called
+//   explicitly.
+// * It is not copyable, but must be explicitly copied using clonePtr().
+// * Temporaries cannot be dereferenced using operator* or operator->.
+template <typename T>
+class MOZ_IS_REFPTR MOZ_TRIVIAL_ABI SafeRefPtr {
+  template <typename U>
+  friend class SafeRefPtr;
+
+  template <typename U, typename... Args>
+  friend SafeRefPtr<U> mozilla::MakeSafeRefPtr(Args&&... aArgs);
+
+  T* MOZ_OWNING_REF mRawPtr = nullptr;
+
+  // BEGIN Some things copied from RefPtr.
+  // We cannot simply use a RefPtr member because we want to be trivial_abi,
+  // which RefPtr is not.
+  void assign_with_AddRef(T* aRawPtr) {
+    if (aRawPtr) {
+      ConstRemovingRefPtrTraits<T>::AddRef(aRawPtr);
+    }
+    assign_assuming_AddRef(aRawPtr);
+  }
+
+  void assign_assuming_AddRef(T* aNewPtr) {
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    if (oldPtr) {
+      ConstRemovingRefPtrTraits<T>::Release(oldPtr);
+    }
+  }
+
+  template <class U>
+  struct ConstRemovingRefPtrTraits {
+    static void AddRef(U* aPtr) { mozilla::RefPtrTraits<U>::AddRef(aPtr); }
+    static void Release(U* aPtr) { mozilla::RefPtrTraits<U>::Release(aPtr); }
+  };
+  template <class U>
+  struct ConstRemovingRefPtrTraits<const U> {
+    static void AddRef(const U* aPtr) {
+      mozilla::RefPtrTraits<U>::AddRef(const_cast<U*>(aPtr));
+    }
+    static void Release(const U* aPtr) {
+      mozilla::RefPtrTraits<U>::Release(const_cast<U*>(aPtr));
+    }
+  };
+  // END Some things copied from RefPtr.
+
+  SafeRefPtr(T* aRawPtr, mozilla::detail::InitialConstructionTag);
+
+ public:
+  SafeRefPtr() = default;
+
+  template <typename U,
+            typename = std::enable_if_t<std::is_convertible_v<U*, T*>>>
+  MOZ_IMPLICIT SafeRefPtr(SafeRefPtr<U>&& aSrc) : mRawPtr(aSrc.mRawPtr) {
+    aSrc.mRawPtr = nullptr;
+  }
+
+  explicit SafeRefPtr(RefPtr<T>&& aRefPtr) : mRawPtr(aRefPtr.forget().take()) {}
+
+  // To prevent implicit conversion of raw pointer to RefPtr and then
+  // calling the previous overload.
+  SafeRefPtr(T* const aRawPtr) = delete;
+
+  SafeRefPtr(T* const aRawPtr, const AcquireStrongRefFromRawPtr&) {
+    assign_with_AddRef(aRawPtr);
+  }
+
+  MOZ_IMPLICIT SafeRefPtr(std::nullptr_t) {}
+
+  // Prevent implicit copying, use clonePtr() instead.
+  SafeRefPtr(const SafeRefPtr&) = delete;
+  SafeRefPtr& operator=(const SafeRefPtr&) = delete;
+
+  // Allow moving.
+  SafeRefPtr(SafeRefPtr&& aOther) noexcept : mRawPtr(aOther.mRawPtr) {
+    aOther.mRawPtr = nullptr;
+  }
+  SafeRefPtr& operator=(SafeRefPtr&& aOther) noexcept {
+    assign_assuming_AddRef(aOther.forget().take());
+    return *this;
+  }
+
+  ~SafeRefPtr() {
+    static_assert(!std::is_copy_constructible_v<T>);
+    static_assert(!std::is_copy_assignable_v<T>);
+    static_assert(!std::is_move_constructible_v<T>);
+    static_assert(!std::is_move_assignable_v<T>);
+
+    if (mRawPtr) {
+      ConstRemovingRefPtrTraits<T>::Release(mRawPtr);
+    }
+  }
+
+  typedef T element_type;
+
+  explicit operator bool() const { return mRawPtr; }
+  bool operator!() const { return !mRawPtr; }
+
+  T& operator*() const&& = delete;
+
+  T& operator*() const& {
+    MOZ_ASSERT(mRawPtr);
+    return *mRawPtr;
+  }
+
+  T* operator->() const&& = delete;
+
+  T* operator->() const& MOZ_NO_ADDREF_RELEASE_ON_RETURN {
+    MOZ_ASSERT(mRawPtr);
+    return mRawPtr;
+  }
+
+  Maybe<T&> maybeDeref() const { return ToMaybeRef(mRawPtr); }
+
+  T* unsafeGetRawPtr() const { return mRawPtr; }
+
+  SafeRefPtr<T> clonePtr() const {
+    return SafeRefPtr{mRawPtr, AcquireStrongRefFromRawPtr{}};
+  }
+
+  already_AddRefed<T> forget() {
+    auto* const res = mRawPtr;
+    mRawPtr = nullptr;
+    return dont_AddRef(res);
+  }
+
+  bool operator==(const SafeRefPtr<T>& aOther) const {
+    return mRawPtr == aOther.mRawPtr;
+  }
+
+  bool operator!=(const SafeRefPtr<T>& aOther) const {
+    return mRawPtr != aOther.mRawPtr;
+  }
+
+  template <typename U, typename = std::enable_if_t<std::is_base_of_v<T, U>>>
+  SafeRefPtr<U> downcast() && {
+    SafeRefPtr<U> res;
+    res.mRawPtr = static_cast<U*>(mRawPtr);
+    mRawPtr = nullptr;
+    return res;
+  }
+
+  template <typename U>
+  friend RefPtr<U> AsRefPtr(SafeRefPtr<U>&& aSafeRefPtr);
+};
+
+template <typename T>
+SafeRefPtr(RefPtr<T>&&) -> SafeRefPtr<T>;
+
+template <typename T>
+SafeRefPtr(already_AddRefed<T>&&) -> SafeRefPtr<T>;
+
+template <typename T>
+class CheckedUnsafePtr;
+
+template <typename T>
+SafeRefPtr(const CheckedUnsafePtr<T>&, const AcquireStrongRefFromRawPtr&)
+    -> SafeRefPtr<T>;
+
+template <typename T>
+SafeRefPtr<T>::SafeRefPtr(T* aRawPtr, detail::InitialConstructionTag)
+    : mRawPtr(aRawPtr) {
+  if (!std::is_base_of_v<detail::SafeRefCountedBase, T> && mRawPtr) {
+    ConstRemovingRefPtrTraits<T>::AddRef(mRawPtr);
+  }
+}
+
+template <typename T>
+bool operator==(std::nullptr_t aLhs, const SafeRefPtr<T>& aRhs) {
+  return !aRhs;
+}
+
+template <typename T>
+bool operator!=(std::nullptr_t aLhs, const SafeRefPtr<T>& aRhs) {
+  return static_cast<bool>(aRhs);
+}
+
+template <typename T>
+bool operator==(const SafeRefPtr<T>& aLhs, std::nullptr_t aRhs) {
+  return !aLhs;
+}
+
+template <typename T>
+bool operator!=(const SafeRefPtr<T>& aLhs, std::nullptr_t aRhs) {
+  return static_cast<bool>(aLhs);
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator==(T* const aLhs, const SafeRefPtr<U>& aRhs) {
+  return aLhs == aRhs.unsafeGetRawPtr();
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator!=(T* const aLhs, const SafeRefPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator==(const SafeRefPtr<T>& aLhs, U* const aRhs) {
+  return aRhs == aLhs;
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator!=(const SafeRefPtr<T>& aLhs, U* const aRhs) {
+  return aRhs != aLhs;
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator==(const Maybe<T&> aLhs, const SafeRefPtr<U>& aRhs) {
+  return &aLhs.ref() == aRhs.unsafeGetRawPtr();
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator!=(const Maybe<T&> aLhs, const SafeRefPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator==(const SafeRefPtr<T>& aLhs, const Maybe<U&> aRhs) {
+  return aRhs == aLhs;
+}
+
+template <typename T, typename U, typename = std::common_type_t<T*, U*>>
+bool operator!=(const SafeRefPtr<T>& aLhs, const Maybe<U&> aRhs) {
+  return aRhs != aLhs;
+}
+
+template <typename T>
+RefPtr<T> AsRefPtr(SafeRefPtr<T>&& aSafeRefPtr) {
+  return aSafeRefPtr.forget();
+}
+
+template <typename T, typename... Args>
+SafeRefPtr<T> MakeSafeRefPtr(Args&&... aArgs) {
+  return SafeRefPtr{new T(std::forward<Args>(aArgs)...),
+                    detail::InitialConstructionTag{}};
+}
+
+template <typename T>
+void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                                 const SafeRefPtr<T>& aField, const char* aName,
+                                 uint32_t aFlags = 0) {
+  CycleCollectionNoteChild(aCallback, aField.unsafeGetRawPtr(), aName, aFlags);
+}
+
+template <typename T>
+void ImplCycleCollectionUnlink(SafeRefPtr<T>& aField) {
+  aField = nullptr;
+}
+
+namespace detail {
+
+template <typename T, RefCountAtomicity Atomicity>
+SafeRefPtr<T> SafeRefCounted<T, Atomicity>::SafeRefPtrFromThis() {
+  // this actually is safe
+  return {static_cast<T*>(this), AcquireStrongRefFromRawPtr{}};
+}
+
+template <typename T>
+struct CopyablePtr<SafeRefPtr<T>> {
+  SafeRefPtr<T> mPtr;
+
+  explicit CopyablePtr(SafeRefPtr<T> aPtr) : mPtr{std::move(aPtr)} {}
+
+  CopyablePtr(const CopyablePtr& aOther) : mPtr{aOther.mPtr.clonePtr()} {}
+  CopyablePtr& operator=(const CopyablePtr& aOther) {
+    if (this != &aOther) {
+      mPtr = aOther.mPtr.clonePtr();
+    }
+    return *this;
+  }
+  CopyablePtr(CopyablePtr&&) = default;
+  CopyablePtr& operator=(CopyablePtr&&) = default;
+};
+
+}  // namespace detail
+
+namespace dom {
+/// XXX Move this to BindingUtils.h later on
+template <class T, class S>
+inline RefPtr<T> StrongOrRawPtr(SafeRefPtr<S>&& aPtr) {
+  return AsRefPtr(std::move(aPtr));
+}
+
+}  // namespace dom
+
+}  // namespace mozilla
+
+template <class T>
+class nsTObserverArray<mozilla::SafeRefPtr<T>>
+    : public nsAutoTObserverArray<mozilla::SafeRefPtr<T>, 0> {
+ public:
+  using base_type = nsAutoTObserverArray<mozilla::SafeRefPtr<T>, 0>;
+  using size_type = nsTObserverArray_base::size_type;
+
+  // Initialization methods
+  nsTObserverArray() = default;
+
+  // Initialize this array and pre-allocate some number of elements.
+  explicit nsTObserverArray(size_type aCapacity) {
+    base_type::mArray.SetCapacity(aCapacity);
+  }
+
+  nsTObserverArray Clone() const {
+    auto result = nsTObserverArray{};
+    result.mArray = mozilla::TransformIntoNewArray(
+        this->mArray, [](const auto& ptr) { return ptr.clonePtr(); });
+    return result;
+  }
+};
+
+// Use MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED in a 'Class' derived from a
+// 'Super' class which derives from (Atomic)SafeRefCounted, and from some other
+// class using NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING.
+#if defined(NS_BUILD_REFCNT_LOGGING)
+#  define MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED(Class, Super)         \
+    template <typename T, ::mozilla::detail::RefCountAtomicity Atomicity> \
+    friend class ::mozilla::detail::SafeRefCounted;                       \
+    NS_IMETHOD_(MozExternalRefCountType) AddRef() override {              \
+      NS_IMPL_ADDREF_INHERITED_GUTS(Class, Super);                        \
+    }                                                                     \
+    NS_IMETHOD_(MozExternalRefCountType) Release() override {             \
+      NS_IMPL_RELEASE_INHERITED_GUTS(Class, Super);                       \
+    }
+#else  // NS_BUILD_REFCNT_LOGGING
+#  define MOZ_INLINE_DECL_SAFEREFCOUNTING_INHERITED(Class, Super)         \
+    template <typename T, ::mozilla::detail::RefCountAtomicity Atomicity> \
+    friend class ::mozilla::detail::SafeRefCounted;                       \
+    NS_IMETHOD_(MozExternalRefCountType) AddRef() override {              \
+      return Super::AddRef();                                             \
+    }                                                                     \
+    NS_IMETHOD_(MozExternalRefCountType) Release() override {             \
+      return Super::Release();                                            \
+    }
+#endif
+
+#endif