Unfortunate; I distinctly recall that Mac was the one platform that did multi-line ellision correctly. I wonder what changed.

One possibility was that we're being sent a new "ln" field of "1", but I verified that it is still "3".

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/15d7d35c2470c8e276046790fc41d8969419f11e

commit 15d7d35c2470c8e276046790fc41d8969419f11e
Author: Kevin Bailey <krb@chromium.org>
Date: Fri Jan 05 19:45:42 2018

[omnibox cocoa] Only cap height of content line

We began capping the result lines, but we were erroneously capping
both the content and description lines. We only want to cap the
content line, leaving the description line free to expand for
dictionary definitions, etc.

Bug:  798199 
Change-Id: I5fc86a5254facfd5b92f95dcbe10ce94d7bfb9c0
Reviewed-on: https://chromium-review.googlesource.com/850586
Reviewed-by: Rachel Blum <groby@chromium.org>
Commit-Queue: Kevin Bailey <krb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527348}
[modify] https://crrev.com/15d7d35c2470c8e276046790fc41d8969419f11e/chrome/browser/ui/cocoa/omnibox/omnibox_popup_cell.mm

Tested this issue on Mac 10.12.6 using chrome reported version-63.0.3239.108 & latest Canary-65.0.3315.0 as per C#0.
Observed the same behavior i.e no bad spacing / wrapping on suggestions list on omni box when we type 'kerbs' text on both reported & latest canary versions.

mpearson@@
Please find the attached screencast for reference & let us know if we miss any steps to check from our end & confirm on the fix too.

Thnaks..!

Hi jm,

What you showed looks working to me. If you'll look in the original screen-shot, you'll see that the definition is very long, and gets cut off at the end, but that the grey selection area where the definition was supposed to go, is large and poorly used.

In your video, the definition is tiny - half a line maybe - and the grey area matches it, which is what we want.

If you'd like to duplicate the original problem, try typing 'krebs cycle' in the Omnibox. (You might have to enter it a couple times before the back-end sends you the definition.) It generates mpearson's definition for me, and takes up about 3 lines (it depends on how wide your window is.)