When decoding deflate stream fails, we insert a dummy gzip header and try again.

This looks like a workaround that might not be applicable anymore. We should add histograms and see if we can remove this.

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  if (decoding_mode_ == DECODE_MODE_DEFLATE && status == Filter::FILTER_ERROR) {
    // As noted in Mozilla implementation, some servers such as Apache with
    // mod_deflate don't generate zlib headers.
    // See 677409 for instances where this work around is needed.
    // Insert a dummy zlib header and try again.
    if (InsertZlibHeader()) {
      *dest_len = dest_orig_size;
      status = DoInflate(dest_buffer, dest_len);
    }
  }
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