IPC: Add new classes required for attachment brokering.

ipc/attachment_broker.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_ATTACHMENT_BROKER_H_
+#define IPC_ATTACHMENT_BROKER_H_
+
+#include "base/macros.h"
+#include "base/process/process_handle.h"
+#include "ipc/brokerable_attachment.h"
+#include "ipc/ipc_export.h"
+
+namespace IPC {
+
+class AttachmentBroker;
+// Classes that inherit from this abstract base class are capable of
+// communicating with a broker to send and receive attachments to Chrome IPC
+// messages.
+class IPC_EXPORT SupportsAttachmentBrokering {
+ public:
+  // Returns an AttachmentBroker used to broker attachments of IPC messages to
+  // other processes. There must be exactly one AttachmentBroker per process.
+  virtual AttachmentBroker* GetAttachmentBroker() = 0;
+};
+
+// Responsible for brokering attachments to Chrome IPC messages. On platforms
+// that support attachment brokering, every IPC channel should have a reference
+// to a AttachmentBroker.
+class IPC_EXPORT AttachmentBroker {
+ public:
+  AttachmentBroker() {}
+  virtual ~AttachmentBroker() {}
+
+  // Sends |attachment| to |destination_process|. The implementation uses an
+  // IPC::Channel to communicate with the broker process. This may be the same
+  // IPC::Channel that is requesting the brokering of an attachment.
+  virtual void SendAttachmentToProcess(BrokerableAttachment* attachment,
+                                       base::ProcessId destination_process) = 0;
+
+  // Returns whether the attachment was available. If the attachment was
+  // available, populates the output parameter |attachment|. The caller then
+  // becomes the owner of |attachment|.
+  virtual bool GetAttachmentWithId(BrokerableAttachment::AttachmentId id,
+                                   BrokerableAttachment* attachment) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AttachmentBroker);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_ATTACHMENT_BROKER_H_