Move Singleton and related structs to namespace base

base/trace_event/trace_log.h

Index: base/trace_event/trace_log.h
diff --git a/base/trace_event/trace_log.h b/base/trace_event/trace_log.h
index dedebce937e671247e9a0e56a357272c872781b4..de722d001e324a48b84b20bad2821e9e64b8a2b2 100644
--- a/base/trace_event/trace_log.h
+++ b/base/trace_event/trace_log.h
@@ -25,11 +25,11 @@
       TRACE_EVENT_PHASE_INSTANT, name, reinterpret_cast<const void*>(id), \
       extra)
 
+namespace base {
+
 template <typename Type>
 struct DefaultSingletonTraits;
 
-namespace base {
-
 class RefCountedString;
 
 namespace trace_event {