Move Singleton and related structs to namespace base

components/app_modal/app_modal_dialog_queue.h

Index: components/app_modal/app_modal_dialog_queue.h
diff --git a/components/app_modal/app_modal_dialog_queue.h b/components/app_modal/app_modal_dialog_queue.h
index 9fbf143d0b91991b2cdaa5a783cdadda5cdba309..77c85879b273a9c46d7e52a5cde7c519fbe8f924 100644
--- a/components/app_modal/app_modal_dialog_queue.h
+++ b/components/app_modal/app_modal_dialog_queue.h
@@ -9,7 +9,9 @@
 
 #include "base/basictypes.h"
 
+namespace base {
 template <typename T> struct DefaultSingletonTraits;
+}
 
 namespace app_modal {
 
@@ -59,7 +61,7 @@ class AppModalDialogQueue {
   iterator end() { return app_modal_dialog_queue_.end(); }
 
  private:
-  friend struct DefaultSingletonTraits<AppModalDialogQueue>;
+  friend struct base::DefaultSingletonTraits<AppModalDialogQueue>;
 
   AppModalDialogQueue();
   ~AppModalDialogQueue();