Revert of Remove IPC::BrokerableAttachment.

ipc/ipc_message_attachment.h

 // Copyright (c) 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_IPC_MESSAGE_ATTACHMENT_H_
 #define IPC_IPC_MESSAGE_ATTACHMENT_H_
 
 #include "base/files/file.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/pickle.h"
 #include "build/build_config.h"
-#include "ipc/ipc.mojom.h"
 #include "ipc/ipc_export.h"
 
 namespace IPC {
 
 // Auxiliary data sent with |Message|. This can be a platform file descriptor
 // or a mojo |MessagePipe|. |GetType()| returns the type of the subclass.
 class IPC_EXPORT MessageAttachment : public base::Pickle::Attachment {
  public:
-  using Type = mojom::SerializedHandle::Type;
+  enum Type {
+    TYPE_PLATFORM_FILE,          // The instance is |PlatformFileAttachment|.
+    TYPE_MOJO_HANDLE,            // The instance is |MojoHandleAttachment|.
+    TYPE_BROKERABLE_ATTACHMENT,  // The instance is |BrokerableAttachment|.
+  };
 
   virtual Type GetType() const = 0;
 
+#if defined(OS_POSIX)
+  virtual base::PlatformFile TakePlatformFile() = 0;
+#endif  // OS_POSIX
+
  protected:
   friend class base::RefCountedThreadSafe<MessageAttachment>;
   MessageAttachment();
   ~MessageAttachment() override;
 
   DISALLOW_COPY_AND_ASSIGN(MessageAttachment);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_MESSAGE_ATTACHMENT_H_