It's keyboard-accessible on Windows, Linux, and Chrome OS. (Press F6 on Win/Linux, or Ctrl+Back/Forward on Chrome OS, or Alt+Shift+T on either, and then Tab to it.)

Elly, could you fix it on Mac? On Mac there also seems to be an issue with an extra tab stop after the omnibox that does nothing.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb2b2ec44ef20413e122ae374477a2327bef7dff

commit cb2b2ec44ef20413e122ae374477a2327bef7dff
Author: ellyjones <ellyjones@chromium.org>
Date: Fri Jun 24 16:49:42 2016

Location bar: make decorations accessible

This is somewhat tricky, since decorations are not NSViews themselves, but are
NSImages that LocationBarViewMac draws over the AutocompleteTextFieldCell.
To be focusable and visible to VoiceOver, these decorations need corresponding
NSViews, but since LocationBarDecoration is deliberately Views-like instead
of Cocoa-like, converting LocationBarDecoration to be an NSView subclass
is infeasible. Instead, this CL adds the notion of an "accessibility view",
which is a fully transparent but focusable and activateable NSView that is
positioned over the LocationBarDecoration's drawn image. The accessibility
views appear in the VoiceOver heirarchy and are focusable and useable by
keyboard users.

BUG= 613019 

Review-Url: https://codereview.chromium.org/2091063002
Cr-Commit-Position: refs/heads/master@{#401882}

[modify] https://crrev.com/cb2b2ec44ef20413e122ae374477a2327bef7dff/chrome/browser/ui/cocoa/location_bar/location_bar_decoration.h
[modify] https://crrev.com/cb2b2ec44ef20413e122ae374477a2327bef7dff/chrome/browser/ui/cocoa/location_bar/location_bar_decoration.mm
[modify] https://crrev.com/cb2b2ec44ef20413e122ae374477a2327bef7dff/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.h
[modify] https://crrev.com/cb2b2ec44ef20413e122ae374477a2327bef7dff/chrome/browser/ui/cocoa/location_bar/location_bar_view_mac.mm
[modify] https://crrev.com/cb2b2ec44ef20413e122ae374477a2327bef7dff/chrome/browser/ui/cocoa/toolbar/toolbar_controller.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/32f65a0c6b303fe3619bb33ac62f687ab4eb2553

commit 32f65a0c6b303fe3619bb33ac62f687ab4eb2553
Author: ellyjones <ellyjones@chromium.org>
Date: Mon Aug 29 15:20:42 2016

a11y: use decoration tooltip for location bar decoration view a11y title

Use the underlying LocationBarDecoration's tooltip for
DecorationAccessibilityView's accessibility title.

Before: Star icon read by VO as "button, button"
After: Star icon read by VO as "Bookmark this page, button"

BUG= 613019 

Review-Url: https://codereview.chromium.org/2289673003
Cr-Commit-Position: refs/heads/master@{#415012}

[modify] https://crrev.com/32f65a0c6b303fe3619bb33ac62f687ab4eb2553/chrome/browser/ui/cocoa/location_bar/location_bar_decoration.mm

This is implemented now! Hooray :)