Move AttachmentStore ownership to datatype

sync/api/syncable_service.h

Index: sync/api/syncable_service.h
diff --git a/sync/api/syncable_service.h b/sync/api/syncable_service.h
index 81b6018b32afb23a18d939fd8078a528dcf76def..9b68d29eadff0a3c47d7d7ea3dce7714d6af0502 100644
--- a/sync/api/syncable_service.h
+++ b/sync/api/syncable_service.h
@@ -11,6 +11,7 @@
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "sync/api/attachments/attachment_store.h"
 #include "sync/api/sync_change_processor.h"
 #include "sync/api/sync_data.h"
 #include "sync/api/sync_error.h"
@@ -65,6 +66,16 @@ class SYNC_EXPORT SyncableService
       const tracked_objects::Location& from_here,
       const SyncChangeList& change_list) OVERRIDE = 0;
 
+  // Returns AttachmentStore used by datatype. Attachment store is used by sync
+  // when uploading or downloading attachments.
+  // GetAttachmentStore is called right before MergeDataAndStartSyncing. If at
+  // that time GetAttachmentStore returns NULL then datatype is considered not
+  // using attachments and all attempts to upload/download attachments will
+  // fail. Default implementation returns NULL. Datatype that uses sync
+  // attachemnts should create attachment store and implement GetAttachmentStore

[maniscalco, 2014/09/08 21:56:35]

typo: attachemnts

+  // to return pointer to it.
+  virtual scoped_refptr<AttachmentStore> GetAttachmentStore();

[maniscalco, 2014/09/08 21:56:35]

I imagine an implementer of a datatype would wonder about which threads might
invoke the dtor of the attachment store.  Can we (sync) guarantee that we will
only clear scoped_refptr's to AttachmentStore in the datatype's thread?  If so
let's document it here.

+
  protected:
   virtual ~SyncableService();
 };