[Sync] The cryptographer should be able to handle empty or old nigori nodes.

chrome/browser/sync/util/cryptographer.h

 // Copyright (c) 2011 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 164 matching lines @@
   // Setter/getter for whether all current and future datatypes should
   // be encrypted. Once set you cannot unset without reading from a
   // new nigori node.  set_encrypt_everything() emits a notification
   // the first time it's called.
   void set_encrypt_everything();
   bool encrypt_everything() const;
 
   // Return the set of encrypted types.
   syncable::ModelTypeSet GetEncryptedTypes() const;
 
-  // Forwards to SetEncryptedTypes.
-  void SetEncryptedTypesForTest(
+  // Forwards to MergeEncryptedTypes.
+  void MergeEncryptedTypesForTest(
       const syncable::ModelTypeSet& encrypted_types);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(CryptographerTest, PackUnpack);
   typedef std::map<std::string, linked_ptr<const Nigori> > NigoriMap;
 
-  // Changes the set of encrypted types and emits a notification if
-  // necessary.
-  void SetEncryptedTypes(const syncable::ModelTypeSet& encrypted_types);
+  // Merges the given set of encrypted types with the existing set and emits a
+  // notification if necessary.
+  void MergeEncryptedTypes(const syncable::ModelTypeSet& encrypted_types);
 
   void EmitEncryptedTypesChangedNotification();
 
   // Helper method to instantiate Nigori instances for each set of key
   // parameters in |bag| and setting the default encryption key to
   // |default_key_name|.
   void InstallKeys(const std::string& default_key_name,
                    const sync_pb::NigoriKeyBag& bag);
 
   bool AddKeyImpl(Nigori* nigori);
@@ skipping 12 matching lines @@
 
   syncable::ModelTypeSet encrypted_types_;
   bool encrypt_everything_;
 
   DISALLOW_COPY_AND_ASSIGN(Cryptographer);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_UTIL_CRYPTOGRAPHER_H_