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

sync/api/attachments/attachment_service_proxy.cc

Index: sync/api/attachments/attachment_service_proxy.cc
diff --git a/sync/api/attachments/attachment_service_proxy.cc b/sync/api/attachments/attachment_service_proxy.cc
index 6590033df531b2855ccdd0b85d6ac74b38122519..9bc40e5530ca745a403c7e71e0a3032e9792215d 100644
--- a/sync/api/attachments/attachment_service_proxy.cc
+++ b/sync/api/attachments/attachment_service_proxy.cc
@@ -32,15 +32,6 @@
     const scoped_refptr<base::SequencedTaskRunner>& task_runner,
     const AttachmentService::DropCallback& callback,
     const AttachmentService::DropResult& result) {
-  task_runner->PostTask(FROM_HERE, base::Bind(callback, result));
-}
-
-// Invokes |callback| with |result| and |attachments| in the |task_runner|
-// thread.
-void ProxyStoreCallback(
-    const scoped_refptr<base::SequencedTaskRunner>& task_runner,
-    const AttachmentService::StoreCallback& callback,
-    const AttachmentService::StoreResult& result) {
   task_runner->PostTask(FROM_HERE, base::Bind(callback, result));
 }
 
@@ -94,17 +85,11 @@
                                             proxy_callback));
 }
 
-void AttachmentServiceProxy::StoreAttachments(const AttachmentList& attachments,
-                                              const StoreCallback& callback) {
+void AttachmentServiceProxy::OnSyncDataAdd(const SyncData& sync_data) {
   DCHECK(wrapped_task_runner_);
-  StoreCallback proxy_callback = base::Bind(
-      &ProxyStoreCallback, base::MessageLoopProxy::current(), callback);
   wrapped_task_runner_->PostTask(
       FROM_HERE,
-      base::Bind(&AttachmentService::StoreAttachments,
-                 core_,
-                 attachments,
-                 proxy_callback));
+      base::Bind(&AttachmentService::OnSyncDataAdd, core_, sync_data));
 }
 
 void AttachmentServiceProxy::OnSyncDataDelete(const SyncData& sync_data) {
@@ -152,13 +137,11 @@
   wrapped_->DropAttachments(attachment_ids, callback);
 }
 
-void AttachmentServiceProxy::Core::StoreAttachments(
-    const AttachmentList& attachments,
-    const StoreCallback& callback) {
+void AttachmentServiceProxy::Core::OnSyncDataAdd(const SyncData& sync_data) {
   if (!wrapped_) {
     return;
   }
-  wrapped_->StoreAttachments(attachments, callback);
+  wrapped_->OnSyncDataAdd(sync_data);
 }
 
 void AttachmentServiceProxy::Core::OnSyncDataDelete(const SyncData& sync_data) {