Checkpointing some Sync Attachment work. Added SyncAttachment and SyncAttachmentId.

sync/api/sync_attachment.cc

+// Copyright 2013 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/api/sync_attachment.h"
+
+#include "base/logging.h"
+#include "base/memory/ref_counted_memory.h"
+#include "base/rand_util.h"
+
+namespace syncer {
+
+SyncAttachment::~SyncAttachment() {}
+
+// Static.
+scoped_ptr<SyncAttachment> SyncAttachment::Create(
+    const scoped_refptr<base::RefCountedMemory>& bytes) {
+  sync_pb::SyncAttachmentId id;
+  // Only requirement here is that this id must be globally unique.
+  id.set_unique_id(base::RandBytesAsString(16));
+  return CreateWithId(id, bytes);
+}
+
+// Static.
+scoped_ptr<SyncAttachment> SyncAttachment::CreateWithId(
+    const sync_pb::SyncAttachmentId& id,
+    const scoped_refptr<base::RefCountedMemory>& bytes) {
+  return scoped_ptr<SyncAttachment>(new SyncAttachment(id, bytes)).Pass();
+}
+
+const sync_pb::SyncAttachmentId& SyncAttachment::GetId() const { return id_; }
+
+const scoped_refptr<base::RefCountedMemory>& SyncAttachment::GetBytes() const {
+  return bytes_;
+}
+
+SyncAttachment::SyncAttachment(
+    const sync_pb::SyncAttachmentId& id,
+    const scoped_refptr<base::RefCountedMemory>& bytes)
+    : id_(id), bytes_(bytes) {
+  DCHECK(!id.unique_id().empty());
+  DCHECK(bytes);
+}
+
+}  // namespace syncer