[Sync] Initial support for encrypting any datatype (no UI hookup yet).

chrome/browser/sync/util/cryptographer.h

 // Copyright (c) 2010 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 CHROME_BROWSER_SYNC_UTIL_CRYPTOGRAPHER_H_
 #define CHROME_BROWSER_SYNC_UTIL_CRYPTOGRAPHER_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 53 matching lines @@
   // Note that encryption will fail if |message| isn't valid (eg. a required
   // field isn't set).
   bool Encrypt(const ::google::protobuf::MessageLite& message,
                sync_pb::EncryptedData* encrypted) const;
 
   // Decrypts |encrypted| into |message|. Returns true unless decryption fails,
   // or |message| fails to parse the decrypted data.
   bool Decrypt(const sync_pb::EncryptedData& encrypted,
                ::google::protobuf::MessageLite* message) const;
 
+  // Decrypts |encrypted| and returns plaintext decrypted data. If decryption
+  // fails, returns empty string.
+  std::string DecryptToString(const sync_pb::EncryptedData& encrypted) const;
+
   // Encrypts the set of currently known keys into |encrypted|. Returns true if
   // successful.
   bool GetKeys(sync_pb::EncryptedData* encrypted) const;
 
   // Creates a new Nigori instance using |params|. If successful, |params| will
   // become the default encryption key and be used for all future calls to
   // Encrypt.
   bool AddKey(const KeyParams& params);
 
   // Decrypts |encrypted| and uses its contents to initialize Nigori instances.
@@ skipping 43 matching lines @@
   NigoriMap::value_type* default_nigori_;  // The Nigori used for encryption.
 
   scoped_ptr<sync_pb::EncryptedData> pending_keys_;
 
   DISALLOW_COPY_AND_ASSIGN(Cryptographer);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_UTIL_CRYPTOGRAPHER_H_