Move Singleton and related structs to namespace base

ios/web/net/cert_store_impl.h

 // Copyright 2015 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.
 
 #ifndef IOS_WEB_NET_CERT_STORE_IMPL_H_
 #define IOS_WEB_NET_CERT_STORE_IMPL_H_
 
 #include "base/memory/singleton.h"
 #include "ios/web/net/request_tracker_data_memoizing_store.h"
 #include "ios/web/public/cert_store.h"
@@ skipping 10 matching lines @@
   int StoreCert(net::X509Certificate* cert, int group_id) override;
   bool RetrieveCert(int cert_id,
                     scoped_refptr<net::X509Certificate>* cert) override;
   void RemoveCertsForGroup(int group_id) override;
 
  protected:
   CertStoreImpl();
   ~CertStoreImpl() override;
 
  private:
-  friend struct DefaultSingletonTraits<CertStoreImpl>;
+  friend struct base::DefaultSingletonTraits<CertStoreImpl>;
 
   RequestTrackerDataMemoizingStore<net::X509Certificate> store_;
 
   DISALLOW_COPY_AND_ASSIGN(CertStoreImpl);
 };
 
 }  // namespace web
 
 #endif  // IOS_WEB_NET_CERT_STORE_IMPL_H_