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

sync/internal_api/attachments/attachment_service_proxy.cc

 // 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.
 
 #include "sync/internal_api/public/attachments/attachment_service_proxy.h"
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/thread_task_runner_handle.h"
 
@@ skipping 31 matching lines @@
     const scoped_refptr<base::SequencedTaskRunner>& wrapped_task_runner,
     const scoped_refptr<Core>& core)
     : wrapped_task_runner_(wrapped_task_runner), core_(core) {
   DCHECK(wrapped_task_runner_.get());
   DCHECK(core_.get());
 }
 
 AttachmentServiceProxy::~AttachmentServiceProxy() {
 }
 
-AttachmentStore* AttachmentServiceProxy::GetStore() {
-  return NULL;
-}
-
 void AttachmentServiceProxy::GetOrDownloadAttachments(
     const AttachmentIdList& attachment_ids,
     const GetOrDownloadCallback& callback) {
   DCHECK(wrapped_task_runner_.get());
   GetOrDownloadCallback proxy_callback =
       base::Bind(&ProxyGetOrDownloadCallback,
                  base::ThreadTaskRunnerHandle::Get(),
                  callback);
   wrapped_task_runner_->PostTask(
       FROM_HERE,
@@ skipping 12 matching lines @@
 }
 
 AttachmentServiceProxy::Core::Core(
     const base::WeakPtr<syncer::AttachmentService>& wrapped)
     : wrapped_(wrapped) {
 }
 
 AttachmentServiceProxy::Core::~Core() {
 }
 
-AttachmentStore* AttachmentServiceProxy::Core::GetStore() {
-  return NULL;
-}
-
 void AttachmentServiceProxy::Core::GetOrDownloadAttachments(
     const AttachmentIdList& attachment_ids,
     const GetOrDownloadCallback& callback) {
   if (!wrapped_) {
     return;
   }
   wrapped_->GetOrDownloadAttachments(attachment_ids, callback);
 }
 
 void AttachmentServiceProxy::Core::UploadAttachments(
     const AttachmentIdSet& attachment_ids) {
   if (!wrapped_) {
     return;
   }
   wrapped_->UploadAttachments(attachment_ids);
 }
 
 }  // namespace syncer