Cleanup usage of history namespace in components/history

components/history/core/browser/thumbnail_database.cc

Index: components/history/core/browser/thumbnail_database.cc
diff --git a/components/history/core/browser/thumbnail_database.cc b/components/history/core/browser/thumbnail_database.cc
index 551af768e0fa4ae5b18f4284535604ded031c7a9..b7ad4c2df59c05b9a4f827d901ca8e3cbcf81668 100644
--- a/components/history/core/browser/thumbnail_database.cc
+++ b/components/history/core/browser/thumbnail_database.cc
@@ -29,6 +29,8 @@
 #include "base/mac/mac_util.h"
 #endif
 
+namespace history {
+
 // Description of database tables:
 //
 // icon_mapping
@@ -568,8 +570,6 @@ void DatabaseErrorCallback(sql::Connection* db,
 
 }  // namespace
 
-namespace history {
-
 ThumbnailDatabase::IconMappingEnumerator::IconMappingEnumerator() {
 }