Oh, sure, this is almost certainly caused by my change.  Anticipation of this kind of thing is exactly why I was at first trying to make the effect subtle but we opted in the end for a more fully selected background color.  The Expected_video above exhibits the drop-cursor bug being fixed, but it's surely preferable to the new behavior (because it was almost unnoticeable).  So we can revert for a quick fix that does no highlight (as in the video) or I can work to make the text stand out from selection background (as in the screenshot).  To keep the original bug fixed, I will work toward the latter unless the former is found preferable.

 Issue 854570  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9cc3021383c1daeca3d92f6832522ddf2e0a3709

commit 9cc3021383c1daeca3d92f6832522ddf2e0a3709
Author: Orin Jaworski <orinj@chromium.org>
Date: Wed Jun 20 23:01:55 2018

[omnibox] Render replacement drop cursor using selection

The replacement drop cursor was being drawn with a rectangle
in the background selection color but the text was unchanged,
causing contrast problems in some environments.  This fix
renders the text using standard selection machinery so the
background and foreground colors change together.

Bug:  853678 
Change-Id: Ia641ada5100f0b88173ff6b21e776ab686553f96
Reviewed-on: https://chromium-review.googlesource.com/1106697
Commit-Queue: Orin Jaworski <orinj@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569069}
[modify] https://crrev.com/9cc3021383c1daeca3d92f6832522ddf2e0a3709/ui/views/controls/textfield/textfield.cc