[Sync] Add ability to save/restore Nigori to SyncEncryptionHandlerImpl

sync/syncable/model_neutral_mutable_entry.cc

 // Copyright 2013 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/syncable/model_neutral_mutable_entry.h"
 
 #include <string>
 
 #include "sync/internal_api/public/base/unique_position.h"
 #include "sync/syncable/directory.h"
@@ skipping 30 matching lines @@
   }
   trans->TrackChangesTo(kernel.get());
 
   kernel_ = kernel.release();
 }
 
 ModelNeutralMutableEntry::ModelNeutralMutableEntry(BaseWriteTransaction* trans,
                                                    CreateNewTypeRoot,
                                                    ModelType type)
     : Entry(trans), base_write_transaction_(trans) {
-  DCHECK(IsTypeWithClientGeneratedRoot(type));
+  // We allow NIGORI because we allow SyncEncryptionHandler to restore a nigori
+  // across Directory instances (see SyncEncryptionHandler::RestoreNigori).
+  if (type != NIGORI)
+    DCHECK(IsTypeWithClientGeneratedRoot(type));
   Entry same_type_root(trans, GET_TYPE_ROOT, type);
   kernel_ = NULL;
   if (same_type_root.good()) {
     return;  // already have a type root for the given type
   }
 
   scoped_ptr<EntryKernel> kernel(new EntryKernel());
 
   sync_pb::EntitySpecifics specifics;
   AddDefaultFieldValue(type, &specifics);
@@ skipping 363 matching lines @@
 ModelNeutralMutableEntry::ModelNeutralMutableEntry(BaseWriteTransaction* trans)
   : Entry(trans), base_write_transaction_(trans) {}
 
 MetahandleSet* ModelNeutralMutableEntry::GetDirtyIndexHelper() {
   return &dir()->kernel()->dirty_metahandles;
 }
 
 }  // namespace syncable
 
 }  // namespace syncer