Reland #1: IPC: Add attachment brokering support to the message header.

This reland fixes a race condition in the unit test SendHandleTwice that caused
the test to flakily fail, mostly on XP machines. This reland also updates switch
statements to contain a block for the newly added enum
BrokerableAttachment::PLACEHOLDER, which was causing problems with the clang
Windows build.

> 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

TBR=tsepez@chromium.org
BUG=493414

Review URL: https://codereview.chromium.org/1303103002

Cr-Commit-Position: refs/heads/master@{#344933}

1 files changed, 28 insertions, 0 deletions

diff --git a/ipc/placeholder_brokerable_attachment.h b/ipc/placeholder_brokerable_attachment.h
new file mode 100644
index 0000000..7a63c72
--- /dev/null
+++ b/ipc/placeholder_brokerable_attachment.h
@@ -0,0 +1,28 @@
+// 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_