Move small c/b/extensions classes into extensions namespace no.2

chrome/browser/extensions/shell_window_registry.cc

Index: chrome/browser/extensions/shell_window_registry.cc
diff --git a/chrome/browser/extensions/shell_window_registry.cc b/chrome/browser/extensions/shell_window_registry.cc
index e97138df3b96457e7c3d02410b7555d1d9153efa..2bd6fc6cde020a5917e2de8afb8ca91bee7d61eb 100644
--- a/chrome/browser/extensions/shell_window_registry.cc
+++ b/chrome/browser/extensions/shell_window_registry.cc
@@ -9,6 +9,8 @@
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
 
+namespace extensions {
+
 ShellWindowRegistry::ShellWindowRegistry() {}
 
 ShellWindowRegistry::~ShellWindowRegistry() {}
@@ -103,3 +105,5 @@ bool ShellWindowRegistry::Factory::ServiceIsCreatedWithProfile() {
 bool ShellWindowRegistry::Factory::ServiceIsNULLWhileTesting() {
   return false;
 }
+
+}  // namespace extensions