Make members of Singleton<T> private and only visible to the singleton type.

net/socket/client_socket_factory.cc

Index: net/socket/client_socket_factory.cc
diff --git a/net/socket/client_socket_factory.cc b/net/socket/client_socket_factory.cc
index 8965630bd613adcc98480b4ce6b6c405e475c473..1c998c6328bb6b7094280c63cd923c4233ea9e95 100644
--- a/net/socket/client_socket_factory.cc
+++ b/net/socket/client_socket_factory.cc
@@ -4,7 +4,7 @@
 
 #include "net/socket/client_socket_factory.h"
 
-#include "base/singleton.h"
+#include "base/lazy_instance.h"
 #include "build/build_config.h"
 #include "net/socket/client_socket_handle.h"
 #if defined(OS_WIN)
@@ -71,11 +71,14 @@ class DefaultClientSocketFactory : public ClientSocketFactory {
   }
 };
 
+static base::LazyInstance<DefaultClientSocketFactory>
+    g_default_client_socket_factory(base::LINKER_INITIALIZED);
+
 }  // namespace
 
 // static
 ClientSocketFactory* ClientSocketFactory::GetDefaultFactory() {
-  return Singleton<DefaultClientSocketFactory>::get();
+  return g_default_client_socket_factory.Pointer();
 }
 
 // static