decode$1 = function base64VLQ_decode(aStr, aIndex, aOutParam) {
  var strLen = aStr.length;
  var result = 0;
  var shift = 0;
  var continuation, digit;

  do {
    if (aIndex >= strLen) {
      throw new Error("Expected more digits in base 64 VLQ value.");
    }

    digit = base64.decode(aStr.charCodeAt(aIndex++));
    if (digit === -1) {
      throw new Error("Invalid base64 digit: " + aStr.charAt(aIndex - 1));
    }

    continuation = !!(digit & VLQ_CONTINUATION_BIT);
    digit &= VLQ_BASE_MASK;
    result = result + (digit << shift);
    shift += VLQ_BASE_SHIFT;
  } while (continuation);

  aOutParam.value = fromVLQSigned(result);
  aOutParam.rest = aIndex;
}
Decodes the next base 64 VLQ value from the given string and returns the
value and the rest of the string via the out parameter.