Move Singleton and related structs to namespace base

chrome/browser/extensions/extension_system_factory.cc

Index: chrome/browser/extensions/extension_system_factory.cc
diff --git a/chrome/browser/extensions/extension_system_factory.cc b/chrome/browser/extensions/extension_system_factory.cc
index bea8cfbdb06b1e92323cec78f262e5e5633a42ac..18266ffe2e51283a0ff3bded7111b9fe4d5bff33 100644
--- a/chrome/browser/extensions/extension_system_factory.cc
+++ b/chrome/browser/extensions/extension_system_factory.cc
@@ -35,7 +35,7 @@ ExtensionSystemSharedFactory::GetForBrowserContext(
 
 // static
 ExtensionSystemSharedFactory* ExtensionSystemSharedFactory::GetInstance() {
-  return Singleton<ExtensionSystemSharedFactory>::get();
+  return base::Singleton<ExtensionSystemSharedFactory>::get();
 }
 
 ExtensionSystemSharedFactory::ExtensionSystemSharedFactory()
@@ -84,7 +84,7 @@ ExtensionSystem* ExtensionSystemFactory::GetForBrowserContext(
 
 // static
 ExtensionSystemFactory* ExtensionSystemFactory::GetInstance() {
-  return Singleton<ExtensionSystemFactory>::get();
+  return base::Singleton<ExtensionSystemFactory>::get();
 }
 
 ExtensionSystemFactory::ExtensionSystemFactory()