Move Singleton and related structs to namespace base

chrome/browser/sync/test/integration/sync_extension_helper.cc

Index: chrome/browser/sync/test/integration/sync_extension_helper.cc
diff --git a/chrome/browser/sync/test/integration/sync_extension_helper.cc b/chrome/browser/sync/test/integration/sync_extension_helper.cc
index 5fd70c8583ec361ae7d5a821c446ad37c1f0b31f..2b10e2d209a0a4cac6386b627e6e8e1321ee8e98 100644
--- a/chrome/browser/sync/test/integration/sync_extension_helper.cc
+++ b/chrome/browser/sync/test/integration/sync_extension_helper.cc
@@ -52,7 +52,7 @@ bool SyncExtensionHelper::ExtensionState::Equals(
 
 // static
 SyncExtensionHelper* SyncExtensionHelper::GetInstance() {
-  SyncExtensionHelper* instance = Singleton<SyncExtensionHelper>::get();
+  SyncExtensionHelper* instance = base::Singleton<SyncExtensionHelper>::get();
   instance->SetupIfNecessary(sync_datatype_helper::test());
   return instance;
 }