Revert of Remove IPC::BrokerableAttachment.

ipc/brokerable_attachment.h

+// Copyright 2015 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 IPC_BROKERABLE_ATTACHMENT_H_
+#define IPC_BROKERABLE_ATTACHMENT_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <algorithm>
+
+#include "base/macros.h"
+#include "build/build_config.h"
+#include "ipc/ipc_export.h"
+#include "ipc/ipc_message_attachment.h"
+
+namespace IPC {
+
+// This subclass of MessageAttachment requires an AttachmentBroker to be
+// attached to a Chrome IPC message.
+class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
+ public:
+  enum BrokerableType {
+    PLACEHOLDER,
+    WIN_HANDLE,
+    MACH_PORT,
+  };
+
+  // Whether the attachment still needs information from the broker before it
+  // can be used.
+  bool NeedsBrokering() const;
+
+  // Returns TYPE_BROKERABLE_ATTACHMENT
+  Type GetType() const override;
+
+  virtual BrokerableType GetBrokerableType() const = 0;
+
+// MessageAttachment override.
+#if defined(OS_POSIX)
+  base::PlatformFile TakePlatformFile() override;
+#endif  // OS_POSIX
+
+ protected:
+  BrokerableAttachment();
+  ~BrokerableAttachment() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BrokerableAttachment);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_BROKERABLE_ATTACHMENT_H_