Move Singleton and related structs to namespace base

chrome/browser/ui/app_list/app_list_service_cocoa_mac.h

Index: chrome/browser/ui/app_list/app_list_service_cocoa_mac.h
diff --git a/chrome/browser/ui/app_list/app_list_service_cocoa_mac.h b/chrome/browser/ui/app_list/app_list_service_cocoa_mac.h
index ba5f511c632a8c0d7c38960d9a938acb30a47382..9fe0ad1c65e58961eda3a08e61ae46908910cd17 100644
--- a/chrome/browser/ui/app_list/app_list_service_cocoa_mac.h
+++ b/chrome/browser/ui/app_list/app_list_service_cocoa_mac.h
@@ -15,7 +15,7 @@ class AppListControllerDelegateImpl;
 @class AppListWindowController;
 
 template <typename T>
-struct DefaultSingletonTraits;
+struct base::DefaultSingletonTraits;
 
 // AppListServiceCocoaMac shows and hides the Cocoa app list on Mac.
 class AppListServiceCocoaMac : public AppListServiceMac {
@@ -40,7 +40,7 @@ class AppListServiceCocoaMac : public AppListServiceMac {
 
  private:
   friend class test::AppListServiceMacTestApi;
-  friend struct DefaultSingletonTraits<AppListServiceCocoaMac>;
+  friend struct base::DefaultSingletonTraits<AppListServiceCocoaMac>;
 
   AppListServiceCocoaMac();