Store attachment crc in AttachmentStore

sync/internal_api/public/attachments/attachment_util.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_INTERNAL_API_PUBLIC_ATTACHMENTS_ATTACHMENT_UTIL_H_
+#define SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ATTACHMENT_UTIL_H_
+
+#include "base/memory/ref_counted.h"
+
+namespace base {
+class RefCountedMemory;
+}
+
+namespace syncer {
+
+// Return the crc32c of the memory described by |data|.
+//
+// Potentially expensive.
+uint32_t ComputeCrc32c(const scoped_refptr<base::RefCountedMemory>& data);
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ATTACHMENT_UTIL_H_