One more bug found: On locked screen, start chromevox, then click top-left corner of chromevox, then press 'ESC' to return to locked screen. Tapping power button for turning display off will alert "alert screen off" for sequential two times and tapping power button for turning display on will alert "alert screen on" for sequential two times.

After discussing with dtseng@, one solution is "do not focus on lock screen when screen is off". After my investigation, the password line will still be chromevox focused even though it is not keyboard focused, which means it has an orange a11y box. So, chromevox will still speak "password edit text...."

I don't know why it happens. But it happens only when there is no orange box on logged-in user's screen. It seems if there is no current orange box, it will try to focus one. But I am still not quite clear of this.

This is because the webview hosting the locked screen/password text field still becomes active.

One potential solution is to annotate the accessibility node wrapping the aura window.

See
ui/views/accessibility/ax_window_obj_wrapper.cc::Serialize.

 there should be some way to know that the window is invisible. If we can convey that information to ChromeVox, we can ignore any events inside of "invisible" windows. With such an annotation available, I can handle silencing ChromeVox.

AX_STATE_INVISIBLE is the proposed state.

warx@ do you have any CLs ready yet?

I have a CL that is not sending for review yet. I need to first chat with tbuckley about the change.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/38b110ec3981062d81c3e61a3a0508eee0f2f1c2

commit 38b110ec3981062d81c3e61a3a0508eee0f2f1c2
Author: warx <warx@chromium.org>
Date: Mon Feb 06 18:45:30 2017

ChromeVox: Disable following a11y events after screen off alert is received

BUG= 686899 
TEST=turning the screen off works fine. For turning the screen on, the "alert screen on" is missing if chromvox needs to talk back the screen focus for the first time.

Review-Url: https://codereview.chromium.org/2676563003
Cr-Commit-Position: refs/heads/master@{#448324}

[modify] https://crrev.com/38b110ec3981062d81c3e61a3a0508eee0f2f1c2/chrome/browser/ui/ash/chrome_shell_delegate.cc

Request merge to M-57, thanks!

Approving merge to M57 Chrome OS.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6c6c221e6b72bcb4c38463fa22d5c8b0db0415f6

commit 6c6c221e6b72bcb4c38463fa22d5c8b0db0415f6
Author: Qiang Xu <warx@chromium.org>
Date: Tue Feb 07 00:32:09 2017

[Merge to M57] ChromeVox: Disable following a11y events after screen off alert is received

TBR=jamescook@chromium.org, dtseng@chromium.org
BUG= 686899 
TEST=turning the screen off works fine. For turning the screen on, the "alert screen on" is missing if chromvox needs to talk back the screen focus for the first time.

Review-Url: https://codereview.chromium.org/2676563003
Cr-Commit-Position: refs/heads/master@{#448324}
(cherry picked from commit 38b110ec3981062d81c3e61a3a0508eee0f2f1c2)

Review-Url: https://codereview.chromium.org/2679823002 .
Cr-Commit-Position: refs/branch-heads/2987@{#352}
Cr-Branched-From: ad51088c0e8776e8dcd963dbe752c4035ba6dab6-refs/heads/master@{#444943}

[modify] https://crrev.com/6c6c221e6b72bcb4c38463fa22d5c8b0db0415f6/chrome/browser/ui/ash/chrome_shell_delegate.cc

Fix reporter's bug, another bug is tracked at issue 689123