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diff --git a/ipc/glue/ForkServiceChild.h b/ipc/glue/ForkServiceChild.h
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+++ b/ipc/glue/ForkServiceChild.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 __FORKSERVICE_CHILD_H_
+#define __FORKSERVICE_CHILD_H_
+
+#include "base/process_util.h"
+#include "nsIObserver.h"
+#include "nsString.h"
+#include "mozilla/ipc/MiniTransceiver.h"
+#include "mozilla/ipc/LaunchError.h"
+#include "mozilla/Result.h"
+
+#include <sys/types.h>
+#include <poll.h>
+
+namespace mozilla {
+namespace ipc {
+
+class GeckoChildProcessHost;
+
+/**
+ * This is the interface to the fork server.
+ *
+ * When the chrome process calls |ForkServiceChild| to create a new
+ * process, this class send a message to the fork server through a
+ * pipe and get the PID of the new process from the reply.
+ */
+class ForkServiceChild {
+ public:
+  ForkServiceChild(int aFd, GeckoChildProcessHost* aProcess);
+  virtual ~ForkServiceChild();
+
+  /**
+   * Ask the fork server to create a new process with given parameters.
+   *
+   * The fork server uses |base::LaunchApp()| to create a new
+   * content process with the following parameters.
+   *
+   * \param aArgv assigns |argv| of the content process.
+   * \param aEnvMap sets |LaunchOptions::env_map|.
+   * \param aFdsRemap sets |LaunchOptions::fd_to_remap|.
+   * \param aPid returns the PID of the content process created.
+   * \return true if success.
+   */
+  Result<Ok, LaunchError> SendForkNewSubprocess(
+      const nsTArray<nsCString>& aArgv, const nsTArray<EnvVar>& aEnvMap,
+      const nsTArray<FdMapping>& aFdsRemap, pid_t* aPid);
+
+  /**
+   * Create a fork server process and the singleton of this class.
+   *
+   * This function uses |GeckoChildProcessHost| to launch the fork
+   * server, getting the fd of a pipe/socket to the fork server from
+   * it's |IPC::Channel|.
+   */
+  static void StartForkServer();
+  static void StopForkServer();
+  /**
+   * Return the singleton.
+   */
+  static ForkServiceChild* Get() {
+    auto child = sForkServiceChild.get();
+    return child == nullptr || child->mFailed ? nullptr : child;
+  }
+
+ private:
+  // Called when a message is received.
+  void OnMessageReceived(UniquePtr<IPC::Message> message);
+  void OnError();
+
+  UniquePtr<MiniTransceiver> mTcver;
+  static UniquePtr<ForkServiceChild> sForkServiceChild;
+  pid_t mRecvPid;
+  bool mFailed;  // The forkserver has crashed or disconnected.
+  GeckoChildProcessHost* mProcess;
+};
+
+/**
+ * Start a fork server at |xpcom-startup| from the chrome process.
+ */
+class ForkServerLauncher : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  ForkServerLauncher();
+  static already_AddRefed<ForkServerLauncher> Create();
+
+ private:
+  friend class ForkServiceChild;
+  virtual ~ForkServerLauncher();
+
+  static void RestartForkServer();
+
+  static bool mHaveStartedClient;
+  static StaticRefPtr<ForkServerLauncher> mSingleton;
+};
+
+}  // namespace ipc
+}  // namespace mozilla
+
+#endif /* __FORKSERVICE_CHILD_H_ */