$this->t() should be used instead of t() for Drupal 8 version

@Pavan B S: The patch in #2 throws exceptions. The classes you have modified to not use the StringTranslationTrait, so the t() method is not currently available. For an example of how to add it, see RecurlyJsLocalTask.

Re-rolled patch and updated with StringTranslationTrait as mentioned in #3.

This will need to be re-rolled after 2868491 is applied as it alters some of the same lines of code.

Also, from the StringTranslationTrait file:

/**
 * Wrapper methods for \Drupal\Core\StringTranslation\TranslationInterface.
 *
 * Using this trait will add t() and formatPlural() methods to the class. These
 * must be used for every translatable string, similar to how procedural code
 * must use the global functions t() and \Drupal::translation()->formatPlural().
 * This allows string extractor tools to find translatable strings.
 *
 * If the class is capable of injecting services from the container, it should
 * inject the 'string_translation' service and assign it to
 * $this->stringTranslation.
 *
...

Some of the files modified with this patch are services, which are capable of having the "string_translation" service injected, so we should follow the best practice here. I can re-roll the patch to accommodate both changes once the aforementioned issue is merged, so I only have to re-roll this once.

@adamzimmermann #2868491: Replace deprecated usage of SafeMarkup::checkPlain() has been merged.

Re-rolled patch.

Looks good, but the dependency injection bit is still missing. I'll add that and re-roll this patch.

#11 looks good with the dependency injection included.