Unfortunately with NVDA it seems that the shortcut is spoken before the current URL. Oh well.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5140145761be8d00c00a4e1f8f57ca1620b83ff2

commit 5140145761be8d00c00a4e1f8f57ca1620b83ff2
Author: Aaron Leventhal <aleventhal@chromium.org>
Date: Fri Dec 08 17:38:16 2017

Expose omnibox keyboard shortcut to screen reader users

Bug:  792943 
Change-Id: Ic005b46f444bbbf030ae65608f57a20113c53e7c
Reviewed-on: https://chromium-review.googlesource.com/809964
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522811}
[modify] https://crrev.com/5140145761be8d00c00a4e1f8f57ca1620b83ff2/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm
[modify] https://crrev.com/5140145761be8d00c00a4e1f8f57ca1620b83ff2/chrome/browser/ui/views/omnibox/omnibox_view_views.cc
[modify] https://crrev.com/5140145761be8d00c00a4e1f8f57ca1620b83ff2/ui/accessibility/platform/ax_platform_node_mac.mm