Move Singleton and related structs to namespace base

base/trace_event/trace_event_win.h

Index: base/trace_event/trace_event_win.h
diff --git a/base/trace_event/trace_event_win.h b/base/trace_event/trace_event_win.h
index 416136155490f9fd94971b90b0ca4ead8492a69c..83d22d7374894eb7cdaee4b03297f1c0e9dd6852 100644
--- a/base/trace_event/trace_event_win.h
+++ b/base/trace_event/trace_event_win.h
@@ -13,10 +13,12 @@
 #include "base/win/event_trace_provider.h"
 
 // Fwd.
+
+namespace base {
+
 template <typename Type>
 struct StaticMemorySingletonTraits;
 
-namespace base {
 namespace trace_event {
 
 // This EtwTraceProvider subclass implements ETW logging