[Sync] Fix crash in GCP when adding encrypted entry that already exists.

components/sync_driver/generic_change_processor.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 COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_
 #define COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 116 matching lines @@
   //
   // |new_attachments| is an output parameter containing newly added attachments
   // that need to be stored.  This method will append to it.
   syncer::SyncError HandleActionUpdate(
       const syncer::SyncChange& change,
       const std::string& type_str,
       const syncer::WriteTransaction& trans,
       syncer::WriteNode* sync_node,
       syncer::AttachmentIdSet* new_attachments);
 
+  // Handle decryption error encountered when reading existing entry. This
+  // helper funciton is used in HandleActionAdd and HandleActionUpdate.
+  syncer::SyncError HandleDecryptionError(const std::string& type_str,
+                                          const syncer::WriteTransaction& trans,
+                                          syncer::WriteNode* sync_node);
+
   // Begin uploading attachments that have not yet been uploaded to the sync
   // server.
   void UploadAllAttachmentsNotOnServer();
 
   const syncer::ModelType type_;
 
   // The SyncableService this change processor will forward changes on to.
   const base::WeakPtr<syncer::SyncableService> local_service_;
 
   // A SyncMergeResult used to track the changes made during association. The
@@ skipping 26 matching lines @@
       attachment_service_weak_ptr_factory_;
   syncer::AttachmentServiceProxy attachment_service_proxy_;
   base::WeakPtrFactory<GenericChangeProcessor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GenericChangeProcessor);
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_