Move Singleton and related structs to namespace base

components/feedback/feedback_uploader_factory.h

Index: components/feedback/feedback_uploader_factory.h
diff --git a/components/feedback/feedback_uploader_factory.h b/components/feedback/feedback_uploader_factory.h
index 13e9ee3ff332a6c3b20e21fbc8ddb86c614357f7..ae99d370e0a511c24876e28198824c295335175e 100644
--- a/components/feedback/feedback_uploader_factory.h
+++ b/components/feedback/feedback_uploader_factory.h
@@ -7,7 +7,9 @@
 
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
+namespace base {
 template<typename T> struct DefaultSingletonTraits;
+}
 
 namespace content {
 class BrowserContext;
@@ -28,7 +30,7 @@ class FeedbackUploaderFactory : public BrowserContextKeyedServiceFactory {
       content::BrowserContext* context);
 
  private:
-  friend struct DefaultSingletonTraits<FeedbackUploaderFactory>;
+  friend struct base::DefaultSingletonTraits<FeedbackUploaderFactory>;
 
   FeedbackUploaderFactory();
   ~FeedbackUploaderFactory() override;