Store attachment crc in AttachmentStore

sync/internal_api/public/attachments/attachment_util.h

Index: sync/internal_api/public/attachments/attachment_util.h
diff --git a/sync/internal_api/public/attachments/attachment_util.h b/sync/internal_api/public/attachments/attachment_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..c0e503ec445d8ce301c62461d2a7db4f04f0fbf7
--- /dev/null
+++ b/sync/internal_api/public/attachments/attachment_util.h
@@ -0,0 +1,28 @@
+// 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"
+#include "sync/base/sync_export.h"
+
+namespace base {
+class RefCountedMemory;
+}
+
+namespace syncer {
+
+// Return the crc32c of the memory described by |data|.
+//
+// Potentially expensive.
+// Ideally this function should be static function in Attachment class, but
+// include_rules from sync/api/DEPS don't allow direct dependency on
+// third_party.
+SYNC_EXPORT_PRIVATE uint32_t
+ComputeCrc32c(const scoped_refptr<base::RefCountedMemory>& data);
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ATTACHMENT_UTIL_H_