Revert of IPC: Add attachment brokering support to the message header. (patchset #20 id:420001 of https://codereview.chromium.org/1286253002/ )

Reason for revert:
Suspected of breaking XP Tests. See, for example https://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/39586 .

Original issue's description:
> IPC: Add attachment brokering support to the message header.
>
> Message dispatch happens before message translation, and message dispatch
> requires that all brokered attachments have been received. This means that
> attachment brokering needs to function without message translation. This is
> accomplished by modifying the message header to include a new field
> num_brokered_attachments, and writing the attachment ids into the IPC Channel
> immediately following the pickled message itself.
>
> AttachmentBrokerPrivilegedWinUnittest was expanded to test ChannelReader in the
> receiving process. It is now a fully functional end-to-end test of attachment
> brokering.
>
> BUG=493414
>
> Committed: https://crrev.com/e8e4f4fa67ee9db6c2910020ef49318e5df68481
> Cr-Commit-Position: refs/heads/master@{#344389}

TBR=tsepez@chromium.org,thakis@chromium.org,erikchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=493414

Review URL: https://codereview.chromium.org/1286883003

Cr-Commit-Position: refs/heads/master@{#344461}

1 files changed, 0 insertions, 28 deletions

diff --git a/ipc/placeholder_brokerable_attachment.h b/ipc/placeholder_brokerable_attachment.h
deleted file mode 100644
index 7a63c72..0000000
--- a/ipc/placeholder_brokerable_attachment.h
+++ /dev/null
@@ -1,28 +0,0 @@
-// 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_PLACEHOLDER_BROKERABLE_ATTACHMENT_H_
-#define IPC_PLACEHOLDER_BROKERABLE_ATTACHMENT_H_
-
-#include "ipc/brokerable_attachment.h"
-#include "ipc/ipc_export.h"
-
-namespace IPC {
-
-// This subclass of BrokerableAttachment has an AttachmentId, and nothing else.
-// It is intended to be replaced by the attachment broker.
-class IPC_EXPORT PlaceholderBrokerableAttachment : public BrokerableAttachment {
- public:
-  PlaceholderBrokerableAttachment(const AttachmentId& id)
-      : BrokerableAttachment(id){};
-  BrokerableType GetBrokerableType() const override;
-
- protected:
-  ~PlaceholderBrokerableAttachment() override{};
-  DISALLOW_COPY_AND_ASSIGN(PlaceholderBrokerableAttachment);
-};
-
-}  // namespace IPC
-
-#endif  // IPC_PLACEHOLDER_BROKERABLE_ATTACHMENT_H_