BTW, is this a regression?

It looks like the normalizing input filter for ChromeOS is triggering mistakenly. ChromeOS maps Alt+Backspace to Delete, and we undo that mapping back to Backspace (otherwise we end up injecting Alt+Backspace). I'll try to work out why it's started being applied to the synthetic C-A-D sequence we inject.

 Issue 611814  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b221cf7b2a66075467ce1184d68bac0e0b0e7614

commit b221cf7b2a66075467ce1184d68bac0e0b0e7614
Author: jamiewalch <jamiewalch@chromium.org>
Date: Sat May 14 01:02:12 2016

Inject synthetic key events later in the input pipeline.

There is already a comment in the code explaining that this is to ensure
that they are not mapped or trapped, but https://codereview.chromium.org/1760633003
reordered the pipeline so that it was no longer correct. As a result, the
Alt+Delete -> Alt+Backspace mapping in the normalizing input filter for
ChromeOS was triggering.

BUG= 611251 

Review-Url: https://codereview.chromium.org/1973413004
Cr-Commit-Position: refs/heads/master@{#393715}

[modify] https://crrev.com/b221cf7b2a66075467ce1184d68bac0e0b0e7614/remoting/client/plugin/chromoting_instance.cc

Requesting merge to M-51. This change only affects Chrome Remote Desktop; there are no changes to Chrome itself.

Your change meets the bar and is auto-approved for M51 (branch: 2704)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bd019e9b426a2414a98706531463701b3b85225b

commit bd019e9b426a2414a98706531463701b3b85225b
Author: Jamie Walch <jamiewalch@chromium.org>
Date: Mon May 16 16:45:25 2016

Inject synthetic key events later in the input pipeline.

There is already a comment in the code explaining that this is to ensure
that they are not mapped or trapped, but https://codereview.chromium.org/1760633003
reordered the pipeline so that it was no longer correct. As a result, the
Alt+Delete -> Alt+Backspace mapping in the normalizing input filter for
ChromeOS was triggering.

BUG= 611251 

Review-Url: https://codereview.chromium.org/1973413004
Cr-Commit-Position: refs/heads/master@{#393715}
(cherry picked from commit b221cf7b2a66075467ce1184d68bac0e0b0e7614)

Review URL: https://codereview.chromium.org/1980063002 .

Cr-Commit-Position: refs/branch-heads/2704@{#555}
Cr-Branched-From: 6e53600def8f60d8c632fadc70d7c1939ccea347-refs/heads/master@{#386251}

[modify] https://crrev.com/bd019e9b426a2414a98706531463701b3b85225b/remoting/client/plugin/chromoting_instance.cc

#CBC-RS/TC-watchlist

ctrl alt del works on Chrome OS with this fix. Verified in client app version 51.0.2704.53

There should be minimal other changes in this app, so I think a quick P0 test pass should be sufficient before pushing it to 10%.

SGTM

 Issue 614012  has been merged into this issue.