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

chrome/browser/chromeos/login/signed_settings_helper.cc

Index: chrome/browser/chromeos/login/signed_settings_helper.cc
diff --git a/chrome/browser/chromeos/login/signed_settings_helper.cc b/chrome/browser/chromeos/login/signed_settings_helper.cc
index b2075f726347adc8b728277eba737405d756f780..a5e53dd24642a5d0eb75eb6f715146a1c7bf968d 100644
--- a/chrome/browser/chromeos/login/signed_settings_helper.cc
+++ b/chrome/browser/chromeos/login/signed_settings_helper.cc
@@ -7,9 +7,9 @@
 #include <string>
 #include <vector>
 
+#include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/ref_counted.h"
-#include "base/singleton.h"
 #include "chrome/browser/browser_thread.h"
 #include "chrome/browser/chromeos/login/signed_settings.h"
 
@@ -309,10 +309,13 @@ class SignedSettingsHelperImpl : public SignedSettingsHelper,
 
   std::vector<OpContext*> pending_contexts_;
 
-  friend struct DefaultSingletonTraits<SignedSettingsHelperImpl>;
+  friend struct base::DefaultLazyInstanceTraits<SignedSettingsHelperImpl>;
   DISALLOW_COPY_AND_ASSIGN(SignedSettingsHelperImpl);
 };
 
+static base::LazyInstance<SignedSettingsHelperImpl>
+    g_signed_settings_helper_impl(base::LINKER_INITIALIZED);
+
 SignedSettingsHelperImpl::SignedSettingsHelperImpl() {
 }
 
@@ -418,7 +421,7 @@ void SignedSettingsHelperImpl::OnOpCompleted(OpContext* context) {
 }
 
 SignedSettingsHelper* SignedSettingsHelper::Get() {
-  return Singleton<SignedSettingsHelperImpl>::get();
+  return g_signed_settings_helper_impl.Pointer();
 }
 
 }  // namespace chromeos