MD History: Use iron-a11y-announcer to announce search result messages

MD History: Use iron-a11y-announcer to announce search result messages

The existing method we were using, `announceAccessibleMethod`, did
not correctly announce messages on Canary, possibly due to timing
issues. iron-a11y-announcer appears to be more robust for making
sure messages are actually announced, since they do not immediately
disappear from the DOM tree.

BUG=606527, 653764
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2399213004
Cr-Commit-Position: refs/heads/master@{#423949}
(cherry picked from commit 2a2797cc88833b227a24dfd476cb9ce125b07004)

Committed: https://chromium.googlesource.com/chromium/src/+/44445bebac9e04a16653f5038f338d0ef2e6c5c2

[tsergeant, 2016-10-10 21:40:33]

Description was changed from

==========
MD History: Use iron-a11y-announcer to announce search result messages

The existing method we were using, `announceAccessibleMethod`, did
not correctly announce messages on Canary, possibly due to timing
issues. iron-a11y-announcer appears to be more robust for making
sure messages are actually announced, since they do not immediately
disappear from the DOM tree.

BUG=606527,653764
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2399213004
Cr-Commit-Position: refs/heads/master@{#423949}
(cherry picked from commit 2a2797cc88833b227a24dfd476cb9ce125b07004)
==========

to

==========
MD History: Use iron-a11y-announcer to announce search result messages

The existing method we were using, `announceAccessibleMethod`, did
not correctly announce messages on Canary, possibly due to timing
issues. iron-a11y-announcer appears to be more robust for making
sure messages are actually announced, since they do not immediately
disappear from the DOM tree.

BUG=606527,653764
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2399213004
Cr-Commit-Position: refs/heads/master@{#423949}
(cherry picked from commit 2a2797cc88833b227a24dfd476cb9ce125b07004)

Committed:
https://chromium.googlesource.com/chromium/src/+/44445bebac9e04a16653f5038f33...
==========

[tsergeant, 2016-10-10 21:40:36]

Committed patchset #1 (id:1) manually as
44445bebac9e04a16653f5038f338d0ef2e6c5c2.

[Dan Beam, 2016-10-11 00:21:05]

dbeam@chromium.org changed reviewers:
+ dbeam@chromium.org

[Dan Beam, 2016-10-11 00:21:05]

lgtm