Reland #1: Clean up interface of attachment broker.

ipc/ipc_channel_win.cc

Index: ipc/ipc_channel_win.cc
diff --git a/ipc/ipc_channel_win.cc b/ipc/ipc_channel_win.cc
index f59f046772e44fa410b2eda5bd1cca1411558789..1442f7fab7b095392510dbe6509c618c49cbffbc 100644
--- a/ipc/ipc_channel_win.cc
+++ b/ipc/ipc_channel_win.cc
@@ -247,6 +247,10 @@ base::ProcessId ChannelWin::GetSenderPID() {
   return GetPeerPID();
 }
 
+bool ChannelWin::IsAttachmentBrokerEndpoint() {
+  return is_attachment_broker_endpoint();
+}
+
 bool ChannelWin::DidEmptyInputBuffers() {
   // We don't need to do anything here.
   return true;