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diff --git a/ipc/mscom/AgileReference.h b/ipc/mscom/AgileReference.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_mscom_AgileReference_h
+#define mozilla_mscom_AgileReference_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupportsImpl.h"
+
+#include <objidl.h>
+
+namespace mozilla {
+namespace mscom {
+namespace detail {
+
+class MOZ_HEAP_CLASS GlobalInterfaceTableCookie final {
+ public:
+  GlobalInterfaceTableCookie(IUnknown* aObject, REFIID aIid,
+                             HRESULT& aOutHResult);
+
+  bool IsValid() const { return !!mCookie; }
+  HRESULT GetInterface(REFIID aIid, void** aOutInterface) const;
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(GlobalInterfaceTableCookie)
+
+  GlobalInterfaceTableCookie(const GlobalInterfaceTableCookie&) = delete;
+  GlobalInterfaceTableCookie(GlobalInterfaceTableCookie&&) = delete;
+
+  GlobalInterfaceTableCookie& operator=(const GlobalInterfaceTableCookie&) =
+      delete;
+  GlobalInterfaceTableCookie& operator=(GlobalInterfaceTableCookie&&) = delete;
+
+ private:
+  ~GlobalInterfaceTableCookie();
+
+ private:
+  DWORD mCookie;
+
+ private:
+  static IGlobalInterfaceTable* ObtainGit();
+};
+
+}  // namespace detail
+
+/**
+ * This class encapsulates an "agile reference." These are references that
+ * allow you to pass COM interfaces between apartments. When you have an
+ * interface that you would like to pass between apartments, you wrap that
+ * interface in an AgileReference and pass the agile reference instead. Then
+ * you unwrap the interface by calling AgileReference::Resolve.
+ *
+ * Sample usage:
+ *
+ * // In the multithreaded apartment, foo is an IFoo*
+ * auto myAgileRef = MakeUnique<AgileReference>(IID_IFoo, foo);
+ *
+ * // myAgileRef is passed to our main thread, which runs in a single-threaded
+ * // apartment:
+ *
+ * RefPtr<IFoo> foo;
+ * HRESULT hr = myAgileRef->Resolve(IID_IFoo, getter_AddRefs(foo));
+ * // Now foo may be called from the main thread
+ */
+class AgileReference final {
+ public:
+  AgileReference();
+
+  template <typename InterfaceT>
+  explicit AgileReference(RefPtr<InterfaceT>& aObject)
+      : AgileReference(__uuidof(InterfaceT), aObject) {}
+
+  AgileReference(REFIID aIid, IUnknown* aObject);
+
+  AgileReference(const AgileReference& aOther) = default;
+  AgileReference(AgileReference&& aOther);
+
+  ~AgileReference();
+
+  explicit operator bool() const {
+    return mAgileRef || (mGitCookie && mGitCookie->IsValid());
+  }
+
+  HRESULT GetHResult() const { return mHResult; }
+
+  template <typename T>
+  void Assign(const RefPtr<T>& aOther) {
+    Assign(__uuidof(T), aOther);
+  }
+
+  template <typename T>
+  AgileReference& operator=(const RefPtr<T>& aOther) {
+    Assign(aOther);
+    return *this;
+  }
+
+  HRESULT Resolve(REFIID aIid, void** aOutInterface) const;
+
+  AgileReference& operator=(const AgileReference& aOther);
+  AgileReference& operator=(AgileReference&& aOther);
+
+  AgileReference& operator=(decltype(nullptr)) {
+    Clear();
+    return *this;
+  }
+
+  void Clear();
+
+ private:
+  void Assign(REFIID aIid, IUnknown* aObject);
+  void AssignInternal(IUnknown* aObject);
+
+ private:
+  IID mIid;
+  RefPtr<IAgileReference> mAgileRef;
+  RefPtr<detail::GlobalInterfaceTableCookie> mGitCookie;
+  HRESULT mHResult;
+};
+
+}  // namespace mscom
+}  // namespace mozilla
+
+template <typename T>
+RefPtr<T>::RefPtr(const mozilla::mscom::AgileReference& aAgileRef)
+    : mRawPtr(nullptr) {
+  (*this) = aAgileRef;
+}
+
+template <typename T>
+RefPtr<T>& RefPtr<T>::operator=(
+    const mozilla::mscom::AgileReference& aAgileRef) {
+  void* newRawPtr;
+  if (FAILED(aAgileRef.Resolve(__uuidof(T), &newRawPtr))) {
+    newRawPtr = nullptr;
+  }
+  assign_assuming_AddRef(static_cast<T*>(newRawPtr));
+  return *this;
+}
+
+#endif  // mozilla_mscom_AgileReference_h