Keep track of which attachments are referenced by which sync entries.

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 <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 80 matching lines @@
   virtual bool SyncModelHasUserCreatedNodes(syncer::ModelType type,
                                             bool* has_nodes);
   virtual bool CryptoReadyIfNecessary(syncer::ModelType type);
 
  protected:
   // ChangeProcessor interface.
   virtual void StartImpl() OVERRIDE;  // Does nothing.
   virtual syncer::UserShare* share_handle() const OVERRIDE;
 
  private:
-  // Helper methods for acting on changes coming from the datatype. These are
-  // logically part of ProcessSyncChanges.
+  // Logically part of ProcessSyncChanges.
+  //
+  // |new_attachments| is an output parameter containing newly added attachments
+  // that need to be stored.  This method will append to it.
   syncer::SyncError HandleActionAdd(const syncer::SyncChange& change,
                                     const std::string& type_str,
                                     const syncer::ModelType& type,
                                     const syncer::WriteTransaction& trans,
-                                    syncer::WriteNode* sync_node);
+                                    syncer::WriteNode* sync_node,
+                                    syncer::AttachmentList* new_attachments);
+
+  // Logically part of ProcessSyncChanges.
+  //
+  // |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::ModelType& type,
                                        const syncer::WriteTransaction& trans,
-                                       syncer::WriteNode* sync_node);
+                                       syncer::WriteNode* sync_node,
+                                       syncer::AttachmentList* new_attachments);
 
   // 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
   // owner will invalidate the weak pointer when association is complete. While
   // the pointer is valid though, we increment it with any changes received
   // via ProcessSyncChanges.
   const base::WeakPtr<syncer::SyncMergeResult> merge_result_;
 
@@ skipping 16 matching lines @@
   base::WeakPtrFactory<syncer::AttachmentService>
       attachment_service_weak_ptr_factory_;
   syncer::AttachmentServiceProxy attachment_service_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(GenericChangeProcessor);
 };
 
 }  // namespace browser_sync
 
 #endif  // COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_