IPC: Remove unnecessary conversions of BrokerableAttachment.

ipc/attachment_broker_unprivileged_win.cc

Index: ipc/attachment_broker_unprivileged_win.cc
diff --git a/ipc/attachment_broker_unprivileged_win.cc b/ipc/attachment_broker_unprivileged_win.cc
index e1d9941f50782e916eeb461363c9925afb1b529b..9e9e7b2145528ab8d4a42801ed554554fea3a988 100644
--- a/ipc/attachment_broker_unprivileged_win.cc
+++ b/ipc/attachment_broker_unprivileged_win.cc
@@ -17,12 +17,12 @@ AttachmentBrokerUnprivilegedWin::AttachmentBrokerUnprivilegedWin() {}
 AttachmentBrokerUnprivilegedWin::~AttachmentBrokerUnprivilegedWin() {}
 
 bool AttachmentBrokerUnprivilegedWin::SendAttachmentToProcess(
-    BrokerableAttachment* attachment,
+    const scoped_refptr<BrokerableAttachment>& attachment,
     base::ProcessId destination_process) {
   switch (attachment->GetBrokerableType()) {
     case BrokerableAttachment::WIN_HANDLE: {
       const internal::HandleAttachmentWin* handle_attachment =
-          static_cast<const internal::HandleAttachmentWin*>(attachment);
+          static_cast<const internal::HandleAttachmentWin*>(attachment.get());
       internal::HandleAttachmentWin::WireFormat format =
           handle_attachment->GetWireFormat(destination_process);
       return get_sender()->Send(