SnapshotMergeReported: add retrofit and cow image size am: 2294f39e

    // Number of reboots that occurred after issuing and before completing the

    // merge of all the snapshot devices.

    optional int32 intermediate_reboots = 3;

    // The device has been upgraded to Virtual A/B.

    optional bool is_vab_retrofit = 4;

    // Space that has been temporarily allocated in the /data partition

    // containing the dm-snapshot's copy-on-write data generated during a

    // Virtual A/B update.

    optional int64 cow_file_size_bytes = 5;

}

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