Have each SandboxedProcessLauncherDelegate maintain a zygote.

content/public/common/zygote_handle.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_PUBLIC_COMMON_ZYGOTE_HANDLE_H_
+#define CONTENT_PUBLIC_COMMON_ZYGOTE_HANDLE_H_
+
+#include <cstddef>
+
+#include "build/build_config.h"
+
+namespace content {
+
+#if defined(OS_POSIX) && !defined(OS_ANDROID) && !defined(OS_MACOSX)
+class ZygoteCommunication;
+using ZygoteHandle = ZygoteCommunication*;
+#else
+using ZygoteHandle = std::nullptr_t;
+#endif
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_COMMON_ZYGOTE_HANDLE_H_