Merge "Fix unsigned type sub overflow issue when isntall DSU" am: 747aa9a4

        // To make sure the alignment doesn't create too much inconsistency, we

        // account the *actual* size, not the requested size.

        total_bytes_written += writer->size();

        remaining_bytes -= writer->size();

        // writer->size() is block size aligned and could be bigger than remaining_bytes

        // If remaining_bytes is bigger, set remaining_bytes to 0 to avoid underflow error.

        remaining_bytes = remaining_bytes > writer->size() ? (remaining_bytes - writer->size()) : 0;

        out->AddFile(std::move(writer));

    }