Clean up public interface of AttachmentBrokerUnprivileged.

ipc/attachment_broker.h

Index: ipc/attachment_broker.h
diff --git a/ipc/attachment_broker.h b/ipc/attachment_broker.h
index 4cf1ab5de587c6407aeb26f7ab478f4000a08eee..e498bb21dfb66e3aef38c22de5ccda6999d7aee7 100644
--- a/ipc/attachment_broker.h
+++ b/ipc/attachment_broker.h
@@ -97,6 +97,13 @@ class IPC_EXPORT AttachmentBroker : public Listener {
   virtual void RegisterCommunicationChannel(Endpoint* endpoint);
   virtual void DeregisterCommunicationChannel(Endpoint* endpoint);
 
+  // In each unprivileged process, exactly one channel should be used to
+  // communicate brokerable attachments with the broker process.
+  virtual void DesignateBrokerCommunicationChannel(Endpoint* endpoint);
+
+  // True if and only if this broker is privileged.
+  virtual bool IsPrivilegedBroker();
+
  protected:
   using AttachmentVector = std::vector<scoped_refptr<BrokerableAttachment>>;