function assignmentOperatorToBinaryOperator(type) {
  switch (type) {
    case STAR_EQUAL:
      return STAR;
    case STAR_STAR_EQUAL:
      return STAR_STAR;
    case SLASH_EQUAL:
      return SLASH;
    case PERCENT_EQUAL:
      return PERCENT;
    case PLUS_EQUAL:
      return PLUS;
    case MINUS_EQUAL:
      return MINUS;
    case LEFT_SHIFT_EQUAL:
      return LEFT_SHIFT;
    case RIGHT_SHIFT_EQUAL:
      return RIGHT_SHIFT;
    case UNSIGNED_RIGHT_SHIFT_EQUAL:
      return UNSIGNED_RIGHT_SHIFT;
    case AMPERSAND_EQUAL:
      return AMPERSAND;
    case CARET_EQUAL:
      return CARET;
    case BAR_EQUAL:
      return BAR;
    default:
      throw Error('unreachable');
  }
}
Returns the binary operator that the assignment operator should use. For
example *= should use *.