Revert of ipc: Clean up interface of attachment broker.

ipc/attachment_broker_unprivileged.h

Index: ipc/attachment_broker_unprivileged.h
diff --git a/ipc/attachment_broker_unprivileged.h b/ipc/attachment_broker_unprivileged.h
index a5437361fe3f3d4737631680415ae2d0c9cd2208..3d98d495932d59ed98d6950d658c00b6a7944362 100644
--- a/ipc/attachment_broker_unprivileged.h
+++ b/ipc/attachment_broker_unprivileged.h
@@ -10,7 +10,6 @@
 
 namespace IPC {
 
-class Channel;
 class Sender;
 
 // This abstract subclass of AttachmentBroker is intended for use in
@@ -20,9 +19,7 @@
   AttachmentBrokerUnprivileged();
   ~AttachmentBrokerUnprivileged() override;
 
-  // In each unprivileged process, exactly one channel should be used to
-  // communicate brokerable attachments with the broker process.
-  void DesignateBrokerCommunicationChannel(IPC::Channel* channel);
+  void set_sender(IPC::Sender* sender) { sender_ = sender; }
 
  protected:
   IPC::Sender* get_sender() { return sender_; }