sync: Introduce CryptographerProvider interface

sync/engine/directory_cryptographer_provider.cc

+// 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.
+
+#include "sync/engine/directory_cryptographer_provider.h"
+
+#include "sync/syncable/directory.h"
+#include "sync/syncable/syncable_read_transaction.h"
+
+namespace syncer {
+
+DirectoryCryptographerProvider::DirectoryCryptographerProvider(
+    syncable::Directory* dir)
+    : dir_(dir) {
+}
+
+DirectoryCryptographerProvider::~DirectoryCryptographerProvider() {
+}
+
+bool DirectoryCryptographerProvider::InitScopedCryptographerRef(
+    ScopedCryptographerRef* scoped) {
+  scoped->Initialize(new ScopedDirectoryCryptographerInternal(dir_));
+  return scoped->IsValid();
+}
+
+ScopedDirectoryCryptographerInternal::ScopedDirectoryCryptographerInternal(
+    syncable::Directory* dir)
+    : dir_(dir), trans_(FROM_HERE, dir) {
+}
+
+ScopedDirectoryCryptographerInternal::~ScopedDirectoryCryptographerInternal() {
+}
+
+Cryptographer* ScopedDirectoryCryptographerInternal::Get() const {
+  return dir_->GetCryptographer(&trans_);
+}
+
+}  // namespace syncer