ipc: Create AttachmentBrokerPrivileged and AttachmentBrokerUnprivileged.

ipc/attachment_broker_privileged.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_PRIVILEGED_H_
+#define IPC_ATTACHMENT_BROKER_PRIVILEGED_H_
+
+#include <vector>
+
+#include "ipc/attachment_broker.h"
+#include "ipc/ipc_export.h"
+
+namespace IPC {
+
+class Channel;
+
+// This abstract subclass of AttachmentBroker is intended for use in a
+// privileged process . When unprivileged processes want to send attachments,
+// the attachments get routed through the privileged process, and more
+// specifically, an instance of this class.
+class IPC_EXPORT AttachmentBrokerPrivileged : public IPC::AttachmentBroker {
+ public:
+  AttachmentBrokerPrivileged();
+  ~AttachmentBrokerPrivileged() override;
+
+  // Each unprivileged process should have one IPC channel on which it
+  // communicates attachment information with the broker process. In the broker
+  // process, these channels must be registered and deregistered with the
+  // Attachment Broker as they are created and destroyed.
+  void RegisterCommunicationChannel(Channel* channel);
+  void DeregisterCommunicationChannel(Channel* channel);
+
+ protected:
+  // Returns nullptr if no channel is found.
+  Channel* GetChannelWithProcessId(base::ProcessId id);
+
+ private:
+  std::vector<Channel*> channels_;
+  DISALLOW_COPY_AND_ASSIGN(AttachmentBrokerPrivileged);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_ATTACHMENT_BROKER_PRIVILEGED_H_