Move Singleton and related structs to namespace base

ppapi/proxy/proxy_module.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/proxy/proxy_module.h"
 
 #include "base/memory/singleton.h"
 
 namespace ppapi {
 namespace proxy {
 
 ProxyModule::ProxyModule() {
 }
 
 ProxyModule::~ProxyModule() {
 }
 
 // static
 ProxyModule* ProxyModule::GetInstance() {
-  return Singleton<ProxyModule>::get();
+  return base::Singleton<ProxyModule>::get();
 }
 
 const std::string& ProxyModule::GetFlashCommandLineArgs() {
   return flash_command_line_args_;
 }
 
 void ProxyModule::SetFlashCommandLineArgs(const std::string& args) {
   flash_command_line_args_ = args;
 }
 
 }  // namespace proxy
 }  // namespace ppapi