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

ipc/attachment_broker.cc

Index: ipc/attachment_broker.cc
diff --git a/ipc/attachment_broker.cc b/ipc/attachment_broker.cc
index 7450ec37e43edafbb1b43ed807c1df7b89f7598f..7e04bcd645de09dd4a4a32e3cd8f6198c567926d 100644
--- a/ipc/attachment_broker.cc
+++ b/ipc/attachment_broker.cc
@@ -6,8 +6,23 @@
 
 #include <algorithm>
 
+namespace {
+IPC::AttachmentBroker* g_attachment_broker = nullptr;
+}
+
 namespace IPC {
 
+// static
+void AttachmentBroker::SetGlobal(AttachmentBroker* broker) {
+  CHECK(!g_attachment_broker);
+  g_attachment_broker = broker;
+}
+
+// static
+AttachmentBroker* AttachmentBroker::GetGlobal() {
+  return g_attachment_broker;
+}
+
 AttachmentBroker::AttachmentBroker() {}
 AttachmentBroker::~AttachmentBroker() {}