Clean up public interface of AttachmentBrokerUnprivileged.

remoting/host/desktop_process.cc

Index: remoting/host/desktop_process.cc
diff --git a/remoting/host/desktop_process.cc b/remoting/host/desktop_process.cc
index 749fd657f619dc9ab9b40cc05cd7822b1c387332..e395c23f6aa74754c5451821dbf1bb948a7e1dab 100644
--- a/remoting/host/desktop_process.cc
+++ b/remoting/host/desktop_process.cc
@@ -147,14 +147,10 @@ bool DesktopProcess::Start(
       IPC::ChannelProxy::Create(daemon_channel_name_, IPC::Channel::MODE_CLIENT,
                                 this, io_task_runner.get());
 
-  // Attachment broker may be already created in tests.
-  if (!IPC::AttachmentBroker::GetGlobal())
-    attachment_broker_ = IPC::AttachmentBrokerUnprivileged::CreateBroker();
-
-  if (attachment_broker_) {
-    attachment_broker_->DesignateBrokerCommunicationChannel(
-        daemon_channel_.get());
-  }
+  IPC::AttachmentBrokerUnprivileged::CreateBrokerIfNeeded();
+  IPC::AttachmentBroker* global = IPC::AttachmentBroker::GetGlobal();
+  if (global && !global->IsPrivilegedBroker())
+    global->DesignateBrokerCommunicationChannel(daemon_channel_.get());
 
   // Pass |desktop_pipe| to the daemon.
   daemon_channel_->Send(