This would be fantastic!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6c0b858a61fc872a976b18e63f653d5524992ab3

commit 6c0b858a61fc872a976b18e63f653d5524992ab3
Author: dtseng <dtseng@chromium.org>
Date: Sat Nov 05 00:25:38 2016

Implement support for chorded braille commands

This cl adds a new type of braille command which is a subtype of BRLAPI_PASSDOTS.

Once received, map the raw dot pattern to a command using standard conventions as set implicitly by various generations of braille notetakers, mobile screen readers, and other braille related applications.

Note1: this approach improves on that taken by other clients that patch specific hardware devices upstream in Brltty. We still utilize hardware mappings there in Chrome OS, but will soon pass through any keys that involve the braille space key.

note2: this change depends on my patch against Brltty to extract the raw chords. It is, however, not blocked by the below patch.
https://chromium-review.googlesource.com/#/c/406528/

Only after both patches land, will braille chording work.

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation
BUG= 633671 

Review-Url: https://codereview.chromium.org/2463983002
Cr-Commit-Position: refs/heads/master@{#430083}

[modify] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/browser/extensions/api/braille_display_private/brlapi_keycode_map.cc
[modify] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/browser/resources/chromeos/chromevox/BUILD.gn
[modify] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/browser/resources/chromeos/chromevox/braille/braille_key_types.js
[modify] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/browser/resources/chromeos/chromevox/cvox2/background/background.js
[add] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/browser/resources/chromeos/chromevox/cvox2/background/braille_command_handler.js
[modify] https://crrev.com/6c0b858a61fc872a976b18e63f653d5524992ab3/chrome/common/extensions/api/braille_display_private.idl

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/37d3f95b11c30933eee53ba153f69457ad92c0e0

commit 37d3f95b11c30933eee53ba153f69457ad92c0e0
Author: David Tseng <dtseng@chromium.org>
Date: Wed Nov 02 02:07:40 2016

Adds upstream patch to support braille chording.

BUG= chromium:633671 
TEST=build image; plug in braille display; press various chords; verify output from ChromeVox.

Change-Id: Id146946e3336867d1da944099d672bcf71f80efa
Reviewed-on: https://chromium-review.googlesource.com/406528
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: David Tseng <dtseng@chromium.org>

[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0006-A-bit-of-retain-chords-code-cleanup.-dm.patch
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/brltty-5.4-r1.ebuild
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0002-Hotkey-handling-shouldn-t-interfere-with-non-hotkey-.patch
[modify] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/brltty.bashrc
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0007-Customize-retain-dots-for-Chrome-OS-and-ChromeVox.patch
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0005-Retain-the-chord-key-when-converting-from-a-brltty-t.patch
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0004-Fixes-to-chord-key-retention.-dm.patch
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0003-Add-a-so-far-manually-settable-flag-for-retaining-th.patch
[add] https://crrev.com/37d3f95b11c30933eee53ba153f69457ad92c0e0/app-accessibility/brltty/files/brltty-5.4-r1-0001-The-autorelease-alarm-wasn-t-correctly-cancelled-on-.patch

 Issue 642780  has been merged into this issue.