Revert of [Sync] Refactor AttachmentStore classes. Introduce concept of referrer.

sync/internal_api/attachments/attachment_service_proxy.cc

Index: sync/internal_api/attachments/attachment_service_proxy.cc
diff --git a/sync/internal_api/attachments/attachment_service_proxy.cc b/sync/internal_api/attachments/attachment_service_proxy.cc
index 50b7a64989f08c544f080c348abf872a505d68df..92104ced5dbb6c6124bdbb4d00df445fea7220a7 100644
--- a/sync/internal_api/attachments/attachment_service_proxy.cc
+++ b/sync/internal_api/attachments/attachment_service_proxy.cc
@@ -49,6 +49,10 @@
 AttachmentServiceProxy::~AttachmentServiceProxy() {
 }
 
+AttachmentStore* AttachmentServiceProxy::GetStore() {
+  return NULL;
+}
+
 void AttachmentServiceProxy::GetOrDownloadAttachments(
     const AttachmentIdList& attachment_ids,
     const GetOrDownloadCallback& callback) {
@@ -81,6 +85,10 @@
 AttachmentServiceProxy::Core::~Core() {
 }
 
+AttachmentStore* AttachmentServiceProxy::Core::GetStore() {
+  return NULL;
+}
+
 void AttachmentServiceProxy::Core::GetOrDownloadAttachments(
     const AttachmentIdList& attachment_ids,
     const GetOrDownloadCallback& callback) {