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 b8704bf040f44f2f51e2d1aa14fa6f1f3ad5a850..769ead0ca22071408afc27bcfef273c9baf2c7fa 100644
--- a/ipc/ipc_channel_nacl.cc
+++ b/ipc/ipc_channel_nacl.cc
@@ -130,8 +130,7 @@ 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";
@@ -225,7 +224,7 @@ bool ChannelNacl::Send(Message* message) {
 }
 
 AttachmentBroker* ChannelNacl::GetAttachmentBroker() {
-  return broker_;
+  return nullptr;
 }
 
 void ChannelNacl::DidRecvMsg(scoped_ptr<MessageContents> contents) {