Implement the V2 sandbox in the process launcher.

content/browser/sandbox_parameters_mac.h

+// Copyright 2017 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_BROWSER_SANDBOX_PARAMETERS_MAC_H_
+#define CONTENT_BROWSER_SANDBOX_PARAMETERS_MAC_H_
+
+namespace sandbox {
+class SeatbeltExecClient;
+}
+
+namespace content {
+
+// Populates the |client| with the parameters that the sandbox needs to
+// resolve information that cannot be known at build time, such as
+// the user's home directory.
+void SetupRendererSandboxParameters(sandbox::SeatbeltExecClient* client);
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_SANDBOX_PARAMETERS_MAC_H_