Move Singleton and related structs to namespace base

ios/chrome/browser/google/google_url_tracker_factory.h

Index: ios/chrome/browser/google/google_url_tracker_factory.h
diff --git a/ios/chrome/browser/google/google_url_tracker_factory.h b/ios/chrome/browser/google/google_url_tracker_factory.h
index ef26de561175eb5ce93b4c9186d81ebc5ae3cabf..5fed6451c4d3dae01f01676c0192ddfedf4efe72 100644
--- a/ios/chrome/browser/google/google_url_tracker_factory.h
+++ b/ios/chrome/browser/google/google_url_tracker_factory.h
@@ -9,8 +9,11 @@
 #include "base/memory/scoped_ptr.h"
 #include "components/keyed_service/ios/browser_state_keyed_service_factory.h"
 
+namespace base {
 template <typename T>
 struct DefaultSingletonTraits;
+}  // namespace bas
+
 class GoogleURLTracker;
 
 namespace ios {
@@ -26,7 +29,7 @@ class GoogleURLTrackerFactory : public BrowserStateKeyedServiceFactory {
   static GoogleURLTrackerFactory* GetInstance();
 
  private:
-  friend struct DefaultSingletonTraits<GoogleURLTrackerFactory>;
+  friend struct base::DefaultSingletonTraits<GoogleURLTrackerFactory>;
 
   GoogleURLTrackerFactory();
   ~GoogleURLTrackerFactory() override;