Replace c/b/nss_context by a KeyedService.

components/cert_database/public/cert_database_service.h

+// Copyright 2014 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 COMPONENTS_CERT_DATABASE_PUBLIC_CERT_DATABASE_SERVICE_H_
+#define COMPONENTS_CERT_DATABASE_PUBLIC_CERT_DATABASE_SERVICE_H_
+
+#include <string>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+namespace net {
+class NSSCertDatabase;
+}
+
+namespace cert_database {
+
+class CertDatabaseServiceIOPart;
+
+class CertDatabaseService : public KeyedService {
+ public:
+  typedef base::Callback<void(net::NSSCertDatabase*)> GetCertDBCallback;
+
+  CertDatabaseService(
+      const scoped_refptr<base::SequencedTaskRunner>& io_task_runner);
+  virtual ~CertDatabaseService();
+
+  // This function is for migrating from old users of nss_context. New users
+  // should use GetIOPart();
+  void GetNSSCertDatabase(const GetCertDBCallback& callback);
+
+  // The caller must ensure that the IOPart outlives this object.
+  void SetIOPart(scoped_ptr<CertDatabaseServiceIOPart> io_part);
+
+  base::WeakPtr<CertDatabaseServiceIOPart> GetIOPart();
+
+ private:
+  scoped_refptr<base::SequencedTaskRunner> io_task_runner_;
+
+  // Whether |io_part_| was set. |io_part_| itself can't be checked on the UI
+  // thread.
+  bool is_io_part_set_;
+
+  // This service is owning the IOPart. However, it lives on the IO thread thus

[tbarzic, 2014/10/22 20:38:19]

Maybe mention that the io_part delete task is posted to IO thread from dtor

[pneubeck (no reviews), 2014/10/24 12:51:37]

Done.

+  // ScopedPtr should not be used. We keep a WeakPtr, so that we can copy
+  // further WeakPtrs on the UI thread.
+  base::WeakPtr<CertDatabaseServiceIOPart> io_part_;
+
+  DISALLOW_COPY_AND_ASSIGN(CertDatabaseService);
+};
+
+}  // namespace cert_database
+
+#endif  // COMPONENTS_CERT_DATABASE_PUBLIC_CERT_DATABASE_SERVICE_H_