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

[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}
Committed: https://chromium.googlesource.com/chromium/src/+/6c6c221e6b72bcb4c38463fa22d5c8b0db0415f6

[Qiang(Joe) Xu, 2017-02-07 00:33:08]

Description was changed from

==========
[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)
==========

to

==========
[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}
Committed:
https://chromium.googlesource.com/chromium/src/+/6c6c221e6b72bcb4c38463fa22d5...
==========

[Qiang(Joe) Xu, 2017-02-07 00:33:09]

Committed patchset #1 (id:1) manually as
6c6c221e6b72bcb4c38463fa22d5c8b0db0415f6 (presubmit successful).