Is it possible to declare a Javascript library dependency at Hook.info?
You can define library dependency using hook_requirements(). Then if the library is missing, drupal will automatically shows the error message in status report(admin/reports/status).

Also it will show the error message, when trying to install module without having required library.

You need to define hook_requirements() in your youmodule.install file like below:

/**
 * Implements hook_requirements().
 */
function yourmodule_requirements($phase) {
  $requirements = array();

  if ($phase == 'runtime') {
      $t = get_t();
      $library = libraries_detect('tinymce');
$error_message = isset($library['error message']) ? $library['error message'] : '';

if (empty($library['installed'])) {
  $requirements['tinymce'] = array(
    'title' =&gt; $t('TinyMCE Library'),
    'value' =&gt; $t('Not installed'),
    'severity' =&gt; REQUIREMENT_ERROR,
    'description' =&gt; $t('!error Please download !tinymce, and extract it into the %directory directory.', array(
        '!error' =&gt; $error_message,
        '!vimeo.ga.js' =&gt; l($t('TinyMCE'), $library['vendor url']),
        '%directory' =&gt; 'sites/all/libraries/tinymce',
      )
    ),
  );
}
else {
  $requirements['tinymce'] = array(
    'title' =&gt; $t('TinyMCE Library'),
    'severity' =&gt; REQUIREMENT_OK,
    'value' =&gt; $t('Installed'),
  );
}
  }

  return $requirements;
}