sync: Introduce CryptographerProvider interface

sync/engine/cryptographer_provider.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 SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_
+#define SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "sync/base/sync_export.h"
+
+namespace syncer {
+
+class Cryptographer;
+class ScopedCryptographerRef;
+class ScopedCryptographerInternal;
+
+// An interface for providing clients with a ScopedCryptographerRef.
+//
+// Used to expose the syncable::Directory's cryptographer to clients that
+// would otherwise not have access to the Directory.
+class SYNC_EXPORT_PRIVATE CryptographerProvider {
+ public:
+  CryptographerProvider();
+  virtual ~CryptographerProvider();
+
+  virtual bool InitScopedCryptographerRef(ScopedCryptographerRef* scoped) = 0;
+};
+
+// A concrete class representing a reference to a cryptographer.
+//
+// Access to the cryptographer is lost when this class goes out of scope.
+class SYNC_EXPORT_PRIVATE ScopedCryptographerRef {
+ public:
+  ScopedCryptographerRef();
+  ~ScopedCryptographerRef();
+
+  bool Initialize(ScopedCryptographerInternal* impl);
+  bool IsValid() const;
+  Cryptographer* Get() const;
+
+ private:
+  scoped_ptr<ScopedCryptographerInternal> scoped_cryptographer_internal_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedCryptographerRef);
+};
+
+// An interface class used in the implementation of the ScopedCryptographerRef.
+//
+// We use this class to allow different implementations of
+// CryptographerProvider to implement InitScopedCryptographer in different
+// ways.  The ScopedCryptographerRef itself must be stack-allocated, so it
+// can't vary depending on which kind of CryptographerProvider is used to
+// intialize it.
+class SYNC_EXPORT_PRIVATE ScopedCryptographerInternal {
+ public:
+  ScopedCryptographerInternal();
+  virtual ~ScopedCryptographerInternal();
+
+  virtual Cryptographer* Get() const = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_CRYPTOGRAPHER_PROVIDER_H_