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

components/sync_driver/generic_change_processor.h

Index: components/sync_driver/generic_change_processor.h
diff --git a/components/sync_driver/generic_change_processor.h b/components/sync_driver/generic_change_processor.h
index a5e33cbc769286ee2d7c0ea382dcf37f3836d67b..789a6344ff29bc407db78e24877779933d4901e6 100644
--- a/components/sync_driver/generic_change_processor.h
+++ b/components/sync_driver/generic_change_processor.h
@@ -98,18 +98,28 @@ class GenericChangeProcessor : public ChangeProcessor,
   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::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);
+
+  // 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::AttachmentList* new_attachments);
 
   // The SyncableService this change processor will forward changes on to.
   const base::WeakPtr<syncer::SyncableService> local_service_;