ipc: Use a global for the process's attachment broker.

ipc/ipc_channel_nacl.cc

Index: ipc/ipc_channel_nacl.cc
diff --git a/ipc/ipc_channel_nacl.cc b/ipc/ipc_channel_nacl.cc
index 2e5f8b32fcd05bb2f87d0939f4c46c999bb295a1..a8457d36f75406eb49587ff1a3bb049f71b06906 100644
--- a/ipc/ipc_channel_nacl.cc
+++ b/ipc/ipc_channel_nacl.cc
@@ -129,8 +129,7 @@ ChannelNacl::ChannelNacl(const IPC::ChannelHandle& channel_handle,
       waiting_connect_(true),
       pipe_(-1),
       pipe_name_(channel_handle.name),
-      weak_ptr_factory_(this),
-      broker_(broker) {
+      weak_ptr_factory_(this) {
   if (!CreatePipe(channel_handle)) {
     // The pipe may have been closed already.
     const char *modestr = (mode_ & MODE_SERVER_FLAG) ? "server" : "client";
@@ -223,7 +222,7 @@ bool ChannelNacl::Send(Message* message) {
 }
 
 AttachmentBroker* ChannelNacl::GetAttachmentBroker() {
-  return broker_;
+  return nullptr;
 }
 
 void ChannelNacl::DidRecvMsg(scoped_ptr<MessageContents> contents) {