IPC: Remove unnecessary conversions of BrokerableAttachment.

ipc/attachment_broker_unprivileged_win.h

Index: ipc/attachment_broker_unprivileged_win.h
diff --git a/ipc/attachment_broker_unprivileged_win.h b/ipc/attachment_broker_unprivileged_win.h
index bcb1500a70059f4aa0c5103e984c3b3f8359de5d..9fa15ee0edb2123b5fed990a458192dc7315a829 100644
--- a/ipc/attachment_broker_unprivileged_win.h
+++ b/ipc/attachment_broker_unprivileged_win.h
@@ -22,8 +22,9 @@ class IPC_EXPORT AttachmentBrokerUnprivilegedWin
   ~AttachmentBrokerUnprivilegedWin() override;
 
   // IPC::AttachmentBroker overrides.
-  bool SendAttachmentToProcess(BrokerableAttachment* attachment,
-                               base::ProcessId destination_process) override;
+  bool SendAttachmentToProcess(
+      const scoped_refptr<BrokerableAttachment>& attachment,
+      base::ProcessId destination_process) override;
 
   // IPC::Listener overrides.
   bool OnMessageReceived(const Message& message) override;