ipc: Move AttachmentBrokerPrivileged singleton logic into ipc/.

ipc/attachment_broker_privileged.cc

Index: ipc/attachment_broker_privileged.cc
diff --git a/ipc/attachment_broker_privileged.cc b/ipc/attachment_broker_privileged.cc
index 0fb9ead006d9a3234b79d8a37681c68081999537..f3e89dc798a15cdb8b6c949eea68228d6870b903 100644
--- a/ipc/attachment_broker_privileged.cc
+++ b/ipc/attachment_broker_privileged.cc
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 
+#include "base/lazy_instance.h"
 #include "base/metrics/histogram_macros.h"
 #include "ipc/ipc_endpoint.h"
 
@@ -19,17 +20,15 @@
 
 namespace IPC {
 
-AttachmentBrokerPrivileged::AttachmentBrokerPrivileged() {
-  IPC::AttachmentBroker::SetGlobal(this);
-}
-
-AttachmentBrokerPrivileged::~AttachmentBrokerPrivileged() {
-  IPC::AttachmentBroker::SetGlobal(nullptr);
-}
+namespace {
 
-// static
-scoped_ptr<AttachmentBrokerPrivileged>
-AttachmentBrokerPrivileged::CreateBroker() {
+// On platforms that support attachment brokering, returns a new instance of
+// a platform-specific attachment broker. Otherwise returns |nullptr|.
+// The caller takes ownership of the newly created instance, and is
+// responsible for ensuring that the attachment broker lives longer than
+// every IPC::Channel. The new instance automatically registers itself as the
+// global attachment broker.
+scoped_ptr<AttachmentBrokerPrivileged> CreateBroker() {
 #if defined(OS_WIN)
   return scoped_ptr<AttachmentBrokerPrivileged>(
       new IPC::AttachmentBrokerPrivilegedWin);
@@ -41,6 +40,37 @@ AttachmentBrokerPrivileged::CreateBroker() {
 #endif
 }
 
+// This class is wrapped in a singleton to ensure that its constructor is only
+// called once. The constructor creates an attachment broker and
+// sets it as the global broker.

[Tom Sepez, 2015/10/21 20:07:38]

Can't lazy instance take care of this for us?

[erikchen, 2015/10/21 21:54:41]

I do use a LazyInstance - I updated the comment to use the word LazyInstance
instead of singleton.

+class AttachmentBrokerMakeOnce {
+ public:
+  AttachmentBrokerMakeOnce() {
+    attachment_broker_.reset(CreateBroker().release());
+  }
+
+ private:
+  scoped_ptr<IPC::AttachmentBrokerPrivileged> attachment_broker_;
+};
+
+base::LazyInstance<AttachmentBrokerMakeOnce>::Leaky
+    g_attachment_broker_make_once = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+AttachmentBrokerPrivileged::AttachmentBrokerPrivileged() {
+  IPC::AttachmentBroker::SetGlobal(this);
+}
+
+AttachmentBrokerPrivileged::~AttachmentBrokerPrivileged() {
+  IPC::AttachmentBroker::SetGlobal(nullptr);
+}
+
+// static
+void AttachmentBrokerPrivileged::CreateBrokerIfNeeded() {
+  g_attachment_broker_make_once.Get();
+}
+
 void AttachmentBrokerPrivileged::RegisterCommunicationChannel(
     Endpoint* endpoint) {
   endpoint->SetAttachmentBrokerEndpoint(true);