Update sync API to support attachments.

sync/api/attachments/attachment_service_proxy.h

+// 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.
+
+#ifndef SYNC_API_ATTACHMENTS_ATTACHMENT_SERVICE_PROXY_H_
+#define SYNC_API_ATTACHMENTS_ATTACHMENT_SERVICE_PROXY_H_
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "base/task_runner.h"
+#include "sync/api/attachments/attachment.h"
+#include "sync/api/attachments/attachment_service.h"
+#include "sync/base/sync_export.h"
+
+namespace syncer {
+
+class SyncData;
+
+// AttachmentServiceProxy wraps an AttachmentService allowing multiple threads
+// to share the wrapped AttachmentService.
+//
+// Callbacks passed to methods on this class will be invoked in the same thread
+// from which the method was called.
+//
+// This class does not own its wrapped AttachmentService object.  This class
+// holds a WeakPtr to the wrapped object.  Once the the wrapped object is
+// destroyed, method calls on this object will be no-ops.
+//
+//  Users of this class should take care to destroy the wrapped object on the
+//  correct thread (wrapped_task_runner).
+//
+// This class is thread-safe.
+class SYNC_EXPORT AttachmentServiceProxy
+    : public AttachmentService,
+      public base::RefCountedThreadSafe<AttachmentServiceProxy> {

[tim (not reviewing), 2014/03/27 17:01:44]

I still think having a hidden ref-counted core object is preferable to make ASP
is easier to use.  The core would own the weak ptr and live on the AS thread,
and would allow ASP to not inherit RefCountedThreadSafe.

[tim (not reviewing), 2014/03/27 17:02:09]

Ignore this comment.  It was stale from before a few of our whiteboard
discussions.

+ public:
+  // Construct an AttachmentServiceProxy that forwards calls to |wrapped| on the
+  // |wrapped_task_runner| thread.
+  AttachmentServiceProxy(
+      const scoped_refptr<base::SequencedTaskRunner>& wrapped_task_runner,
+      base::WeakPtr<syncer::AttachmentService> wrapped);
+
+  // AttachmentService implementation.
+  virtual void GetOrDownloadAttachments(const AttachmentIdList& attachment_ids,
+                                        const GetOrDownloadCallback& callback)
+      OVERRIDE;
+  virtual void DropAttachments(const AttachmentIdList& attachment_ids,
+                               const DropCallback& callback) OVERRIDE;
+  virtual void OnSyncDataAdd(const SyncData& sync_data) OVERRIDE;
+  virtual void OnSyncDataDelete(const SyncData& sync_data) OVERRIDE;
+  virtual void OnSyncDataUpdate(const AttachmentIdList& old_attachment_ids,
+                                const SyncData& updated_sync_data) OVERRIDE;
+  virtual base::WeakPtr<AttachmentService> AsWeakPtr() OVERRIDE;
+
+ private:
+  friend class base::RefCountedThreadSafe<AttachmentServiceProxy>;
+
+  scoped_refptr<base::SequencedTaskRunner> wrapped_task_runner_;
+  // wrapped_ must only be dereferenced on the wrapped_task_runner_ thread.
+  base::WeakPtr<AttachmentService> wrapped_;
+
+  // Must be last data member.
+  base::WeakPtrFactory<AttachmentService> weak_ptr_factory_;
+
+  virtual ~AttachmentServiceProxy();
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_SERVICE_PROXY_H_