Add an ellipsis to truncated comment titles

#tstoeckler This patch doesn't apply on my system. Following error is thrown :

Checking patch core/modules/comment/src/CommentForm.php...
warning: core/modules/comment/src/CommentForm.php has type 100755, expected 100644
error: while searching for:
      // 2) Strip out all HTML tags
      // 3) Convert entities back to plain-text.
      $comment_text = $comment->comment_body->processed;
      $comment->setSubject(Unicode::truncate(trim(Html::decodeEntities(strip_tags($comment_text))), 29, TRUE));
      // Edge cases where the comment body is populated only by HTML tags will
      // require a default subject.
      if ($comment->getSubject() == '') {

error: patch failed: core/modules/comment/src/CommentForm.php:301
error: core/modules/comment/src/CommentForm.php: patch does not apply
Checking patch core/modules/comment/src/Tests/CommentInterfaceTest.php...
warning: core/modules/comment/src/Tests/CommentInterfaceTest.php has type 100755, expected 100644
error: while searching for:
    $body_text = 'Lorem ipsum Lorem ipsum Loreming ipsum Lorem ipsum';
    $comment1 = $this->postComment(NULL, $body_text, '', TRUE);
    $this->assertTrue($this->commentExists($comment1), 'Form comment found.');
    $this->assertEqual('Lorem ipsum Lorem ipsum', $comment1->getSubject());

    // Break at 29 characters where there's no boundary before that.
    $body_text2 = 'LoremipsumloremipsumLoremingipsumLoremipsum';
    $comment2 = $this->postComment(NULL, $body_text2, '', TRUE);
    $this->assertEqual('LoremipsumloremipsumLoremingi', $comment2->getSubject());
  }

  /**

error: patch failed: core/modules/comment/src/Tests/CommentInterfaceTest.php:220
error: core/modules/comment/src/Tests/CommentInterfaceTest.php: patch does not apply

I was going through your patch and found that following thing doesn't exist in my files :

 $body_text = 'Lorem ipsum Lorem ipsum Loreming ipsum Lorem ipsum';
-    $this->assertEqual('Lorem ipsum Lorem ipsum', $comment1->getSubject());
     $comment2 = $this->postComment(NULL, $body_text2, '', TRUE);
-    $this->assertEqual('LoremipsumloremipsumLoremingi', $comment2->getSubject());

@tstoeckler, I already have latest code with clean head. I have cross checked it twice. Maybe I am missing with something else. Can you please guide me on it?

The patch in #6 applies cleanly. @Shivam Agarwal: I'm not sure what is causing the errors you're seeing but them seem to be limited to your localhost.

I've tested the patch and verified it works as expected and would move it to RTBC except for the "Needs usability review" tag, which I don't feel qualified to do.

This gets a big +1 from me! Thank you @tstoeckler.

Yes, patch works! Screenshot attached.

Screenshot attached in #13.

Committed b85ec52 and pushed to 8.0.x. Thanks!

Thanks for adding the beta evaluation.